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1.
  • Blixt, Y., et al. (författare)
  • Interlaboratory random amplified polymorphic DNA typing of Yersinia enterocolitica and Y. enterocolitica-like bacteria
  • 2003
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 83:1, s. 15-26
  • Tidskriftsartikel (refereegranskat)abstract
    • A random amplified polymorphic DNA (RAPD) protocol was developed for interlaboratory use to discriminate food-borne Yersinia enterocolitica O:3 from other serogroups of Y. enterocolitica and from Y. enterocolitica-like species. Factors that were studied regarding the RAPD performance were choice of primers and concentration of PCR reagents (template DNA, MgCl 2, primer and Taq DNA polymerase). A factorial design experiment was performed to identify the optimal concentrations of the PCR reagents. The experiment showed that the concentration of the PCR reagents tested significantly affected the number of distinct RAPD products. The RAPD protocol developed was evaluated regarding its discrimination ability using 70 different Yersinia strains. Cluster analysis of the RAPD patterns obtained revealed three main groups representing (i) Y. pseudotuberculosis, (ii) Y. enterocolitica and (iii) Y. kristensenii, Y. frederiksenii, Y. intermedia and Y. ruckeri. Within the Y. enterocolitica group, the European serovar (O:3) and the North American serovar (O:8) could be clearly separated from each other. All Y. enterocolitica O:3 strains were found in one cluster which could be further divided into two subclusters, representing the geographical origin of the isolates. Thus, one of the subclusters contained Y. enterocolitica O:3 strains originating from Sweden, Finland and Norway, while Danish and English O:3 strains were found in another subcluster together with O:9 and O:5,27 strains. The repeatability (intralaboratory) and reproducibility (interlaboratory) of the RAPD protocol were tested using 15 Yersinia strains representing different RAPD patterns. The intralaboratory and the interlaboratory studies gave similarity coefficients of the same magnitude (generally >70%) for the individual strains. In the present study, it was shown that interreproducible RAPD results could be achieved by appropriate optimisation of the RAPD protocol. Furthermore, the study reflects the heterogeneous genetic diversity of the Y. enterocolitica species. © 2002 Elsevier Science B.V. All rights reserved.
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2.
  • Dahlenborg, Maria, et al. (författare)
  • Prevalence of Clostridium botulinum types B, E, and F in faecal samples from Swedish cattle.
  • 2003
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 82:2, s. 105-110
  • Tidskriftsartikel (refereegranskat)abstract
    • Faeces were collected from 60 cows at three slaughterhouses situated in southern and central Sweden. The faecal samples were collected during two sampling periods over the year, summer and winter. All samples were analysed for the presence of Clostridium botulinum spores, according to a combined selection and enrichment PCR procedure. One PCR assay was specific for part of the type B neurotoxin gene, while the other assay was specific for both type E and F neurotoxin genes. The prevalence of C. botulinum in Swedish cattle was established to be 73% for non-proteolytic type B and less than 5% for types E and F. Twenty-eight (64%) of the positive faecal samples had a spore load of less than 4 spores/g. Statistical analysis (ANOVA) showed that seasonal variation (summer and winter) had a significant effect on the prevalence of C. botulinum type B in cattle, whereas the effect of geographical location of rearing of the cattle (southern and central Sweden) was less significant.
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3.
  • Knutsson, Rickard, et al. (författare)
  • Evaluation of selective enrichment PCR procedures for Yersinia enterocolitica.
  • 2002
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 73:1, s. 35-46
  • Tidskriftsartikel (refereegranskat)abstract
    • Four enrichment PCR protocols for detecting unlysed cells of pathogenic Yersinia enterocolitica were studied. First, the probability of detecting Y. enterocolitica cells of known concentrations by a multiplex PCR assay was determined, and it was found to follow a logistic regression model. From this model, the probability of detecting Y enterocolitica at a specific concentration could be estimated; for example, the detection probability of 10(4) CFU/ml was estimated to be 85.4%. The protocols were evaluated on enrichment cultures inoculated with 10(2) CFU/ml Y. enterocolitica and 10(2)-10(6) CFU/ml of a defined background flora. For each protocol, the time for sample withdrawal and the presence of background flora were studied with respect to PCR detection. The optimal point in time of sample withdrawal was found to be different for each protocol employed. Early detection was favoured by concentrating the target cells, and the most rapid PCR detection of Y. enterocolitica was achieved with enrichment in Yersinia-PCR-compatible-enrichment (YPCE) medium for 3 h at 25 degrees C, followed by a centrifugation prior to PCR analysis. For detection of Y. enterocolitica in the presence of high concentrations (10(6) CFU/ml) of background flora, a long incubation time followed by density centrifugation and a dilution step was most successful. The protocol that gave the most reliable PCR detection in the presence of 10(6) CFU/ml background flora included 24 h incubation in Yersinia-selective-enrichment (YSE) broth at 25 degrees C, followed by Percoll density centrifugation, and a 100 times dilution prior to PCR analysis.
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4.
  • Andersson, Annika, et al. (författare)
  • Comparison between automatic ribotyping and random amplified polymorphic DNA analysis of Bacillus cereus isolates from the dairy industry
  • 1999
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 47:42006, s. 147-151
  • Tidskriftsartikel (refereegranskat)abstract
    • Discrimination by automatic ribotyping and random amplified polymorphic DNA PCR, RAPD, was compared for 40 different B. cereus dairy isolates, 4 different B. mycoides isolates and 6 culture collection strains. RAPD-PCR has previously shown to be useful for tracing contamination routes of B. cereus to milk. Automatic ribotyping using EcoRI and PvuII separated the B. cereus and B. mycoides isolates/strains into 36 different ribotypes. RAPD-typing with primers generated 40 different RAPD-profiles. However, 17 isolates clustered into eight groups, irrespective of the primer and restriction enzyme used, and in all but one case, the isolates with the same pattern were isolated from the same dairy. Automatic ribotyping proved to be a useful, standardized and quick method to discriminate between B. cereus strains, only slightly less discriminatory than RAPD-typing.
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5.
  • Andersson, Annika, et al. (författare)
  • The adhesion of Bacillus cereus spores to epithelial cells might be an additional virulence mechanism
  • 1998
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 39:1-2, s. 93-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Four out of ten Bacillus cereus strains produced spores able to adhere to monolayers of Caco-2 cells (human epithelial cells). One of these strains has been involved in an outbreak of food poisoning where the symptoms were more severe and persisted for longer than a normal B. cereus food poisoning. The hydrophobicity of the spores is a contributing factor for the adhesion to occur. The spores are able to germinate in an environment similar to that of the small intestine and then the vegetative cells can produce the enterotoxin directly at the target place. A concentrated and active form of the enterotoxin will be taken up by the epithelial cells in the small intestine. Spore adhesion could be an important virulence factor for some B. cereus strains.
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6.
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7.
  • Andersson, Rolf E. (författare)
  • Inhibition of Staphylococcus aureus and spheroplasts of Gram-negative bacteria by an antagonistic compound produced by a strain of Lactobacillus plantarum
  • 1986
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 3:3, s. 149-160
  • Tidskriftsartikel (refereegranskat)abstract
    • A strain of Lactobacillus plantarum was examined for production of an extracellular antagonistic compound. Cellfree preparations, dialyzed to remove organic acids, were used in inhibition studies which revealed that Gram-positive bacteria were sensitive. Among these, Staphylococcus aureus was chosen for further characterization of the agent. The antagonistic compound was susceptible to breakdown by proteolytic enzymes and its effect was completely lost after heat treatment at 121°C for 15 min. Ultrafiltration studies indicated that the agent had a molecular weight of over 100, 000, suggesting a complex protein-containing aggregate. The antagonistic effect was found to be highest at low pH values and S. aureus was shown to be able to adapt to the agent. Most Gram-negative bacteria were resistant to the compound. However, after their transformation to spheroplasts, which removed most of the cell envelopes, these bacteria were sensitized. The conclusion is that the antagonistic mechanism probably includes agent influence on the cell surface. © 1986.
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8.
  • Andersson, Rolf E. (författare)
  • Nitrate reduction during fermentation by Gram-negative bacterial activity in carrots
  • 1985
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 2:4, s. 219-225
  • Tidskriftsartikel (refereegranskat)abstract
    • Carrots were subjected to lactic acid fermentation through the action of a starter culture, Lactobacillus plantarum, and changes in the amount of both the naturally present and added nitrate were recorded. The nitrate content in the carrots decreased to about 10% of the original amount during the initial stage of the fermentation process. By using irradiation-sterilized carrots it was shown that the decrease in the nitrate content is a result of the activity of the Gram-negative bacteria, which dominate the flora during the initial stage of the fermentation process, and that the lactic acid bacteria present were unable to affect the nitrate content. The nitrite concentration was also determined and was found not to exceed 0.2 mg/kg on any occasion. The conclusion is that if the nitrate content of carrots is to be lowered in a fermentation process, this process must be controlled in such a way as to allow the original Gram-negative flora to reduce the nitrate amount before the starter organism takes over. © 1985.
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9.
  • Aronsson, Kristina, et al. (författare)
  • Growth of pulsed electric field exposed Escherichia coli in relation to inactivation and environmental factors
  • 2004
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 93:1, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Pulsed electric fields (PEF) have been proven to inactivate microorganisms during nonthermal conditions and have the potential to replace thermal processing as a method for food preservation. However, there is a need to understand the recovery and growth of survivors and potentially injured microorganisms following PEF processing. The purpose of this investigation was to study the growth of Escherichia coli at 10°C following exposure to electrical field strengths (15, 22.5 and 30 kV/cm) in relation to inactivation and the amount of potentially sublethally injured cells. One medium was used as both a treatment medium and an incubation medium, to study the influence of environmental factors on the inactivation and the growth of the surviving population. The pH (5.0, 6.0 and 7.0) and water activity (1.00, 0.985 and 0.97) of the medium was varied by adding HCl and glycerol, respectively. Growth was followed continuously by measuring the optical density. The time-to-detection (td) and the maximum specific growth rate (?max) were calculated from these data. Results showed that the PEF process did not cause any obvious sublethal injury to the E. coli cells. The number of survivors was a consequence of the combination of electrical field strength and environmental factors, with pH being the most prominent. Interestingly, the ?max of subsequent growth was influenced by the applied electrical field strength during the process, with an increased ?max at more intense electrical field strengths. In addition, the ?max was also influenced by the pH and water activity. The td, which could theoretically be considered as an increase in shelf life, was found to depend on a complex correlation between electrical field strength, pH and water activity. That could be explained by the fact that the td is a combination of the number of survivors, the recovery of sublethal injured cells and the growth rate of the survivors. © 2003 Published by Elsevier B.V.
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10.
  • Berndtson, Eva, et al. (författare)
  • Campylobacter incidence on a chicken farm and the spread of Campylobacter during the slaughter process
  • 1996
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 32:1-2, s. 35-47
  • Tidskriftsartikel (refereegranskat)abstract
    • To get a better understanding of the epidemiology of Campylobacter, a chicken farm was studied for 16 weeks with samplings in each flock weekly from input until the flock became colonized with Campylobacter or slaughtered. Samples were taken from fresh droppings and from drinkers during the rearing period, as well as from the environment in empty houses. The spread of Campylobacter during the slaughter process was also surveyed. No Campylobacter was found in samples from newly-hatched ol one-week-old chickens or their drinkers. All Hocks but one were colonized at two to five weeks of age. All Campylobacter isolates belonged to the same sero- and biotype; C. jejuni Penner 2. The spread of Campylobacter in the flock was rapid and usually all samples were positive once colonization had been proven. C. jejuni was isolated from flies in ante-rooms as well as from air in chicken units ill houses with positive chicken flocks. Samples were taken at slaughter when some of the Campylobacter positive Hocks from the farm were slaughtered. Campylobacter were isolated from all sampled equipment along the processing line, from the chicken transport crates to the chillers, as well as from the air.
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11.
  • Beuchat, L. R., et al. (författare)
  • Performance of mycological media in enumerating desiccated food spoilage yeasts : an interlaboratory study
  • 2001
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 70:1-2, s. 89-96
  • Tidskriftsartikel (refereegranskat)abstract
    • Dichloran 18% glycerol agar (DG18) was originally formulated to enumerate nonfastidious xerophilic moulds in foods containing rapidly growing Eurotium species. Some laboratories are now using DG18 as a general purpose medium for enumerating yeasts and moulds, although its performance in recovering yeasts from dry foods has not been evaluated. An interlaboratory study compared DG18 with dichloran rose bengal chloramphenicol agar (DRBC), plate count agar supplemented with chloramphenicol (PCAC), tryptone glucose yeast extract chloramphenicol agar (TGYC), acidified potato dextrose agar (APDA), and orange serum agar (OSA) for their suitability to enumerate 14 species of lyophilized yeasts. The coefficient of variation for among-laboratories repeatability within yeast was 1.39% and reproducibility of counts among laboratories was 7.1%. The order of performance of media for recovering yeasts was TGYC > PCAC = OSA > APDA > DRBC > DG18. A second study was done to determine the combined effects of storage time and temperature on viability of yeasts and suitability of media for recovery. Higher viability was retained at - 18 degreesC than at 5 degreesC or 25 degreesC for up to 42 weeks, although the difference in mean counts of yeasts stored at - 18 degreesC and 25 degreesC was only 0.78 log(10) cfu/ml of rehydrated suspension. TGYC was equal to PCAC and superior to the other four media in recovering yeasts stored at - 18 degreesC, 5 degreesC, or 25 degreesC for up to 42 weeks. Results from both the interlaboratory study and the storage study support the use of TGYC for enumerating desiccated yeasts. DG18 is not recommended as a general purpose medium for recovering yeasts from a desiccated condition.
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12.
  • Danielsson-Tham, Marie-Louise, et al. (författare)
  • Characterization of Listeria strains isolated from soft cheese
  • 1993
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 18:2, s. 161-166
  • Tidskriftsartikel (refereegranskat)abstract
    • Three soft cheeses were exposed to quantitative analysis for listeria and found to contain a large number of listeria. Thirty-five of the listeria strains isolated from the three cheeses were characterized by use of biochemical tests, serotyping, phagetyping and DNA restriction enzyme analysis. Seven isolates were identified as Listeria innocuaand 28 as Listeria monocytogenes. Two to four different clones of L. monocytogenescould be identified from each cheese. In contrast, only one clone could be detected among the L. innocua isolates. From an epidemiological point of view the findings of different clones of L. monocytogenes in the same cheese emphasize the need for typing several listeria isolates from one and the same food sample. It is concluded that the best overview of the population of the listeria strains is obtained after direct plating of the sample followed by enumeration, isolation and extensive typing.
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13.
  • Jonsson, A., et al. (författare)
  • Electronic nose for microbial quality classification of grains
  • 1997
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 35:2, s. 187-193
  • Tidskriftsartikel (refereegranskat)abstract
    • The odour of grains is in many countries the primary criterion of fitness for consumption. However, smelling of grain for quality grading should be avoided since inhalation of mould spores or toxins may be hazardous to the health and determinations of the off-odours are subjective. An electronic nose, i.e. a gas sensor array combined with a pattern recognition routine might serve as an alternative. We have used an electronic nose consisting of a sensor array with different types of sensors. The signal pattern from the sensors is collected by a computer and further processed by an artificial neural network (ANN) providing the pattern recognition system. Samples of oats, rye and barley with different odours and wheat with different levels of ergosterol, fungal and bacterial colony forming units (cfu) were heated in a chamber and the gas in the chamber was led over the sensory array. The ANN could predict the odour classes of good, mouldy, weakly and strongly musty oats with a high degree of accuracy. The ANN also indicated the percentage of mouldy barley or rye grains in mixtures with fresh grains. In wheat a high degree of correlation between ANN predictions and measured ergosterol as well as with fungal and bacterial cfu was observed. The electronic nose can be developed to provide a simple and fast method for quality classification of grain and is likely to find applications also in other areas of food mycology.
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14.
  • Loncarevic, Semir, et al. (författare)
  • Occurrence of Listeria monocytogenes in soft and semi-soft cheeses in retail outlets in Sweden
  • 1995
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 26:2, s. 245-250
  • Tidskriftsartikel (refereegranskat)abstract
    • Samples of 333 retail cheeses produced in or imported into Sweden were examined for the presence of Listeria monocytogenes. Listeria monocytogenes was isolated from 6% of the cheese samples. Cheeses made from raw milk were more frequently contaminated with L. monocytogenes (42%) than cheeses made from heat-treated milk (2%). The incidence of the organism in whole cheeses and pre-cut wedges was similar (6%). L. monocytogenes was only found in imported cheeses (18 from France, and one from Germany and Italy, respectively). The numbers of L. monocytogenes varied from < 1 x 10(2) to 1 X 10(5) cfu/g. All L. monocytogenes strains belonged to serogroup 1/2, except isolates from two samples that belonged to serogroup 4.
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15.
  • Lund, Bodil, et al. (författare)
  • Gastrointestinal transit survival of an Enterococcus faecium probiotic strain administered with or without vancomycin
  • 2002
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 77:1-2, s. 109-115
  • Tidskriftsartikel (refereegranskat)abstract
    • The primary aim of this study was to evaluate if an ingested probiotic, containing viable Enterococcus faecium could survive gastrointestinal transit and if so, correlate the amount of the recovered probiotic strain with the host's own enterococci. The second aim was to investigate if simultaneous vancomycin intake influenced the survival and persistence of the probiotic strain and the stability of endogenous enterococci strains. Twenty healthy volunteers were given the probiotic product once daily for 10 days. Half of the subjects were simultaneously given vancomycin. Isolates of E. faecium strains were genotypically or phenotypically analysed with pulsed-field gel electrophoresis (PFGE) and the PhenePlate(TM) system, respectively. In eight of the ten volunteers given only the probiotic, the ingested E. faecium could be detected on day 10, while in none on day 31. From subjects given both probiotic and vancomycin no ingested E. faecium could be detected on day 10 or day 31. The estimated amount of ingested E. faecium recovered from faeces on day 10 ranged from 1.2 x 10(3) to 4.2 x 10(6) colony forming units per gram faeces, which in several cases were a substantial part of the total amount of E. faecium. The E. faecium isolated before probiotic plus vancomycin administration showed no close relationship to the ones isolated 3 weeks after ceased intake in any subjects. In conclusion, the ingested E. faecium strain can survive gastrointestinal transit. After intake, the E. faecium probiotic strain might become a large part of the total E, faecium population. The occurrence of the probiotic strain in the human gut seems to be transient after intake stop. Re-colonization of E. faecium after simultaneous probiotic plus vancomycin intake occurs mainly with strains without close genetic relationship to the strains harboured before treatment or to the ingested E. faecium strain.
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16.
  • Olsson, J., et al. (författare)
  • Detection and quantification of ochratoxin A and deoxynivalenol in barley grains by GC-MS and electronic nose
  • 2002
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 72:3, s. 203-214
  • Tidskriftsartikel (refereegranskat)abstract
    • Mycotoxin contamination of cereal grains can be detected and quantified using complex extraction procedures and analytical techniques. Normally, the grain odour, i.e. the presence of non-grain volatile metabolites, is used for quality classification of grain. We have investigated the possibility of using fungal volatile metabolites as indicators of mycotoxins in grain. Ten barley samples with normal odour, and 30 with some kind of off-odour were selected from Swedish granaries. The samples were evaluated with regard to moisture content, fungal contamination, ergosterol content, and levels of ochratoxin A (OA) and deoxynivalenol (DON). Volatile compounds were also analysed using both an electronic nose and gas chromatography combined with mass spectrometry (GC-MS). Samples with normal odour had no detectable ochratoxin A and average DON contents of 16 mug kg(-1) (range 0-80), while samples with off-odour had average OA contents of 76 mug kg(-1) (range 0-934) and DON contents of 69 mug kg(-1) (range 0-857). Data were evaluated by multivariate data analysis using projection methods such as principal component analysis (PCA) and partial least squares (PLS). The results show that it was possible to classify the OA level as below or above the maximum limit of 5 mug kg(-1) cereal grain established by the Swedish National Food Administration, and that the DON level could be estimated using PLS. Samples with OA levels below 5 mug kg(-1) had higher concentration of aldehydes (nonanal, 2-hexenal) and alcohols (1-penten-3-ol, 1-octanol). Samples with OA levels above 5 mug kg(-1) had higher concentrations of ketones (2-hexanone, 3-octanone). The GC-MS system predicted OA concentrations with a higher accuracy than the electronic nose, since the GC-MS misclassified only 3 of 37 samples and the electronic nose 7 of 37 samples. No correlation was found between odour and OA level, as samples with pronounced or strong off-odours had OA levels both below and above 5 mug kg(-1). We were able to predict DON levels in the naturally contaminated barley samples using the volatile compounds detected and quantified by either GC-MS or the electronic nose. Pentane, methylpyrazine, 3-pentanone, 3-octene-2-ol and isooctylacetate showed a positive correlation with DON, while ethylhexanol, pentadecane, toluene, 1-octanol, 1-nonanol, and 1-heptanol showed a negative correlation with DON. The root mean square error of estimation values for prediction of DON based on GC-MS and electronic nose data were 16 and 25 mug kg(-1) respectively.
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17.
  • Olsson, J., et al. (författare)
  • Volatiles for mycological quality grading of barley grains : determinations using gas chromatography-mass spectrometry and electronic nose
  • 2000
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 59:3, s. 167-178
  • Tidskriftsartikel (refereegranskat)abstract
    • The possibility of using an electronic nose or gas chromatography combined with mass spectrometry (GC-MS) to quantify ergosterol and colony forming units (CFU) of naturally contaminated barley samples was investigated. Each sample was split into three parts for (i) ergosterol and CFU analysis, (ii) measurements with the electronic nose and (iii) identification of volatiles collected on an adsorbent with a GC-MS system. Forty samples were selected after sensory analysis to obtain 10 samples with normal odour and 30 with some degree of off-odour. The data set of volatile compounds and the data collected from the electronic nose were evaluated by multivariate analyse techniques. SIMCA classification (soft independent modelling of class analogy) was used for objective evaluation of the usefulness of the data from the GC-MS or electronic nose measurements for classification of grain samples as normal or with off-odour. The main volatile compounds of grain with normal odour were 2-hexenal, benzaldehyde and nonanal, while 3-octanone, methylheptanone and trimethylbenzene were the main volatile compounds of grain with off-odours. Using data from the electronic nose three samples of 40 were misclassified, while data analysis of the volatile compounds detected with the GC-MS, led to six misclassified samples. Regression models (partial least-squares, PLS) were built to predict ergosterol- and CFU-levels with data from the GC-MS or electronic nose measurements. PLS models based on both GC-MS and electronic nose data could be used to predict the ergosterol levels with high accuracy and with low root mean square error of prediction (RMSEP). CFU values from naturally infected grain could not be predicted with the same degree of confidence.
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18.
  • Suihko, M.-L., et al. (författare)
  • Characterization of Listeria monocytogenes isolates from the meat, poultry and seafood industries by automated ribotyping
  • 2002
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 72:42006, s. 137-146
  • Tidskriftsartikel (refereegranskat)abstract
    • A total of 564 Listeria monocytogenes isolates were characterized by automated ribotyping. The samples were taken from equipment, personnel and the environment after cleaning procedures and during food processing, as well as from raw materials and products from six meat, two poultry and five seafood processing plants located in the Faroe Islands, Finland, Iceland, Norway and Sweden. Altogether, 25 different ribotypes (RTs) were generated. Two RTs occurred in the samples from all three food sectors-meat, poultry and seafood. Four RTs occurred in meat and poultry plant samples and other four RTs occurred in meat and seafood plant samples. Five RTs occurred only in meat plant samples, five only in poultry plant samples and five only in seafood plant samples. Eight of the thirteen plants had their own in-house L. monocytogenes ribotype. There was geographical differences between the RTs, but no correlation between RTs and food sectors was detected. The discrimination power of automated ribotyping was satisfactory to trace the contamination sources in the food processing plants clearly indicating the sites at which improved cleaning procedures were necessary. In addition, it was possible to screen a large number of isolates with two instruments located at different institutes and to make a reliable combination of the results. Copyright © 2002 Elsevier Science B.V.
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19.
  • Söderström, Charlotte, 1973-, et al. (författare)
  • Use of an electronic tongue and HPLC with electrochemical detection to differentiate molds in culture media
  • 2005
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 97:3, s. 247-257
  • Tidskriftsartikel (refereegranskat)abstract
    • A study was conducted to further evaluate an electronic tongue, using high-performance liquid chromatography (HPLC) with electrochemical (EC) and UV detection as a reference method. The electronic tongue consisted of four working electrodes made of different metals and arranged in a standard three-electrode configuration. Pulses of voltage were applied to the metals, and the current responses were sampled and collected in a data matrix. The objectives of the present investigation were to examine the ability of the electronic tongue to distinguish between two mold species growing in three different media, and to obtain support for the hypothesis that the device actually discriminates between different redox-active metabolites produced by the molds. Peak areas in EC and UV HPLC chromatograms were collected in a data matrix. The electronic tongue data and the EC and UV data were then subjected to principal component analysis (PCA). A number of peaks in the HPLC-EC chromatograms indicated that the growth media contained redox-active metabolites. Moreover, PCA of peak areas in EC chromatograms revealed differences between the distribution of redox-active metabolites produced by the two species and between the three culture media. The same pattern was apparent in a PCA score plot of electronic tongue data. The peaks in the UV and EC chromatograms differed, and these were also shown by the PCA score plots.
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20.
  • Söderström, Charlotte, et al. (författare)
  • Use of an electronic tongue to analyze mold growth in liquid media
  • 2003
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 83:3, s. 253-261
  • Tidskriftsartikel (refereegranskat)abstract
    • The feasibility of employing an electronic tongue to measure the growth of mold in a liquid medium was studied. We used the electronic tongue developed at Linköping University, which is based on pulsed voltammetry and consists of an array of different metal electrodes. Instead of focusing on a single parameter, this device provides information about the condition or quality of a sample or process. Accordingly, the data obtained are complex, and multivariate methods such as principal component analysis (PCA) or projection to latent structures (PLS) are required to extract relevant information. A gas chromatographic technique was developed to measure ergosterol content in mold biomass and was subsequently used as a reference method to investigate the ability of the electronic tongue to measure the growth of mold in liquid media. The result shows that the electronic tongue can monitor mold growth in liquids. In PLS analysis, the electronic tongue signals correlate well with the amount of ergosterol in the mold biomass as well as the microbially induced changes in the pH of the medium. © 2002 Elsevier Science B.V. All rights reserved.
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21.
  • Tham, Wilhelm, 1951-, et al. (författare)
  • Histamine formation by enterococci in goat cheese
  • 1990
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 11:3-4, s. 225-229
  • Tidskriftsartikel (refereegranskat)abstract
    • Cheeses were made of heat-treated goat milk inoculated with large numbers of a histamine-producing strain of Streptococcus faecium or a non-histamine-producing strain of S. faecalis. Every second week during ripening (91 days) the cheeses were sampled for histamine analyses and bacteriological analyses. The numbers of enterococci remained high throughout the whole period of investigation and the maximum amount of histamine detected was 8.2-mu-g/g in one of the cheeses. The enterococci seem to have no relevance from a histamine intoxication point of view in cheeses of this kind.
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22.
  • Tham, Wilhelm, 1951- (författare)
  • Histamine formation by enterococci isolated from home-made goat cheeses
  • 1988
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 7:2, s. 103-108
  • Tidskriftsartikel (refereegranskat)abstract
    • A survey was made of the histamine-producing capability of enterococci isolated from goat cheeses. The strains, 130 Streptococcus faecium and 106 S. faecalis, were grown in Trypticase Soy Broth Histidine medium (TSBH) at 35°C for 24 h and the histamine formed was determined by fluorometry. Forty-one (31.5%) of the S. faecium strains and 2 (1.9%) of the S. faecalis strains produced histamine. The largest amount detected was 4.0 μg histamine/ml TSBH. Compared with the amounts of histamine produced by some Gram-negative bacteria, the histamine production by enterococci seems to be low. Under the present conditions the enterococci seem to have no relevance from a histamine intoxication point of view.
  •  
23.
  • Tham, Wilhelm, 1951-, et al. (författare)
  • Lessons from an outbreak of listeriosis related to vacuum-packed gravad and cold-smoked fish
  • 2000
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 62:3, s. 173-175
  • Tidskriftsartikel (refereegranskat)abstract
    • The first lesson learned from this outbreak was that vacuum-packed rainbow trout is not only an excellent medium for the growth of Listeria monocytogenes, but may also cause human listeriosis. Another lesson is that one single fish processing plant may spread multiple clonal types of L. monocytogenes by selling contaminated products to consumers. Thus, when investigating fish-borne outbreaks of listeriosis one should identify and type several isolates of L. monocytogenes from each food and environmental sample, since multiple clonal types might be present. The outbreak described in this paper involved at least eight human cases, three clonal types of L. monocytogenes, and lasted for 11 months. During the outbreak investigation, L. monocytogenes was also isolated from another brand of rainbow trout found in the refrigerator of one of the patients. These latter isolates belonged to a clonal type not associated with the outbreak. However, this clonal type is of considerable interest since it has been associated with foodborne outbreaks of listeriosis in several countries, and is also the second most common clonal type among human clinical isolates of L. monocytogenes in Sweden. Besides the described outbreak, it is likely that vacuum-packed, cold-smoked and gravad rainbow trout have been involved in additional cases of foodborne listeriosis in Sweden.
  •  
24.
  • Thisted Lambertz, Susanne, et al. (författare)
  • A combined culture and PCR method for detection of pathogenic Yersinia enterocolitica in food
  • 2000
  • Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 57:1-2, s. 63-73
  • Tidskriftsartikel (refereegranskat)abstract
    • A combined method based on traditional culturing, buoyant density centrifugation, (BDC), and polymerase chain reaction (PCR) techniques for detection and identification of pathogenic Y. enterocolitica in food was developed and evaluated. An internal control, which was added in each PCR-tube and co-amplified by the same primer pair as the pathogen, monitored false-negative PCR results. The sample preparation step, BDC, was used to remove PCR inhibiting food substances and to concentrate the Y. enterocolitica cells. Single PCR with a chromosomal gene (ail) as target was chosen for screening the samples. The method was tested on naturally and artificially contaminated food samples. In three different food samples, processed meat (brawn), unprocessed beef and minced pork, inoculated with 10 cfu pathogenic Y. enterocolitica per gram, Y. enterocolitica was detected and cultural bacteria indicated within 18 h of enrichment.
  •  
25.
  • Aronsson, Kristina, et al. (författare)
  • Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae in relation to membrane permeabilization and subsequent leakage of intracellular compounds due to pulsed electric field processing
  • 2005
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 99:1, s. 19-32
  • Tidskriftsartikel (refereegranskat)abstract
    • Membrane permeabilization, caused by pulsed electric field (PEF) processing of microbial cells, was investigated by measurement of propidium iodide (PI) uptake with flow cytometry. Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae was determined by viable counts, and leakage of intracellular compounds, such as ATP and UV-absorbing substances, was measured in the extracellular environment. Electrical field strength and pulse duration influenced membrane permeabilization of all three tested organisms of which S. cerevisiae was the most PEF sensitive, followed by E. coli and L. innocua. It was shown by viable counts, PI uptake and leakage of intracellular compounds that L. innocua was the most resistant. Increased inactivation corresponded to greater numbers of permeabilized cells, which were reflected by increased PI uptake and larger amounts of intracellular compounds leaking from cells. For E. coli and L. innocua, a linear relationship was observed between the number of inactivated cells (determined as CFU) and cells with permeated membranes (determined by PI uptake), with higher number of inactivated cells than permeated cells. Increased leakage of intracellular compounds with increasing treatment severity provided further evidence that cells were permeabilized. For S. cerevisiae, there was higher PI uptake after PEF treatments, although very little or no inactivation was observed. Results suggest that E. coli and L. innocua cells, which took up PI, lost their ability to multiply, whereas cells of S. cerevisiae, which also took up PI, were not necessarily lethally permeabilized. © 2004 Elsevier B.V. All rights reserved.
  •  
26.
  • Artursson, Karin, et al. (författare)
  • Foodborne pathogens in unpasteurized milk in Sweden
  • 2018
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 284, s. 120-127
  • Tidskriftsartikel (refereegranskat)abstract
    • Raw milk may be a risk for public health if it is contaminated with zoonotic pathogens. To study the prevalencein unpasteurized milk from Swedish farms, bovine and small ruminant dairy farms were sampled. Since thesampling method and transport conditions may influence the outcome of analyses, efforts were made to optimizethe methodology. Culturing of bacteria was done from in-line milk filters collected from the milk pipe at thepoint where it enters the milk bulk tank at the farms and this way of sampling was compared to sampling bulktank milk (BTM) directly. Analysing milk filters were found to be superior to analysing BTM directly. Conditionsfor transport of milk filter samples were further improved by the addition of Cary Blair transport medium, whichsignificantly increased the number of positive samples for pathogenic bacteria. The isolation of several foodbornepathogens from milk filters was demonstrated. The prevalence of samples with Staphylococcus aureus was71% and 64%, and Listeria spp. 21% and 29% from dairy cow and goat/sheep farms, respectively. Campylobacterjejuni, Yersinia enterocolitica and verotoxigenic Escherichia coli (VTEC) O157 were detected in 9%, 2% and 2% ofsamples from bovine milk, respectively.We conclude that the choice of sampling method and sample handling influence the results of bacterialculturing. From the results of this study, we strongly recommend to sample in-line milk filters instead of BTMdirectly and to use Cary Blair medium during transport, especially if the samples are to be analysed forCampylobacter spp. and/or Listeria spp. The findings also show that unpasteurized milk from Swedish farmsoccasionally contain bacteria with zoonotic potential.
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27.
  • Bakeeva, Albina, et al. (författare)
  • Distribution of mycotoxins produced by Penicillium spp. inoculated in apple jam and creme fraiche during chilled storage
  • 2019
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 292, s. 13-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Estimations of consumer exposure to mycotoxins through surveillance of mycotoxins in the food trade are well described, but the exposure due to mouldy food in private homes is not known, and may result from removing visible mould on food and eating the rest. In this study, we followed the growth of Penicillium expansum on the surface of apple jam and Penicillium verrucosum on creme fraiche, as well as production and distribution of fungal metabolites throughout the sample (approx. 6 cm high divided into three equal layers), using a multianalyte method, over time (up to 28 days) and at 4, 8 and 15 degrees C.Growth rates and apparent lag times for P. expansum in apple jam at different temperatures were estimated by fitting to the Baranyi model. The growth rates were 1.7, 2.7 and 4.3 mm day(-1) for storage at 4, 8 and 15 degrees C, respectively; apparent lag times decreased with increasing storage temperature and were 10.6, 7.9 and 2.6 days at corresponding temperatures. Patulin and roquefortine C were identified and quantified, among other fungal metabolites. Patulin was detected in all 2-cm layers of the apple jam at 15 degrees C. Concentrations in the upper two layers of the jar corresponded to exposures exceeding the health based guidance value (HBGV) for a normal serving size. Consequently, removal of the mouldy part is insufficient to avoid unhealthy exposure. In contrast to patulin, roquefortine C was also produced at 4 degrees C.The growth of P. verrucosum on creme fraiche was very restricted and could not be modelled. Despite the small colony (8 +/- 0.5 mm in diameter), ochratoxin A and citrinin were detected after 21 days at 15 degrees C in the top 2 cm layer (including the fungal colony), and at concentrations in a normal serving corresponding to an exposure above the HBGV established by EFSA for both mycotoxins. Questiomycin A, an antibiotic, was also produced in creme fraiche but in contrast to the two mycotoxins, was detected throughout all layers of the creme fraiche and was produced also at 4 and 8 degrees C.As a complement to a previous study, we also present production and the distribution of major fungal metabolites in apple jam and creme fraiche for some additional fungal strains (P. crustosum, P. roqueforti and P. verrucosum on apple jam and P. expansum on creme fraiche). A pilot study investigating the effect of inoculation size on toxin production may have implications for the best inoculum to use in experimental studies.
  •  
28.
  • Boqvist, Sofia, et al. (författare)
  • Escherichia coli O157:H7 reduction in hamburgers with regard to premature browning of minced beef, colour score and method for determining doneness
  • 2015
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 215, s. 109-116
  • Tidskriftsartikel (refereegranskat)abstract
    • This study investigated the effect of premature browning (PMB) on the survival of Escherichia coli O157:H7 in beef hamburgers after cooking with respect to interior colour of the hamburger and recommendations to cook hamburgers to a core temperature of 71 degrees C. Assessment of doneness by visual inspection or measurement of internal temperature was compared in terms of survival and the increased relative risk of illness due to PMB was estimated. At the last consume-by-day, hamburgers made from minced meat packaged in 80/20 O-2/CO2 (MAP hamburger) and from meat minced at retail packaged in atmospheric condition (control hamburger) were inoculated with a gfp-tagged strain of E. coli O157:H7 (E. coli O157:H7gfp+). Hamburgers were cooked for different times during assessment of the core temperature every 30 s and cut in halves after cooking. Doneness was evaluated based on visual judgement of the internal colour using a score chart (C-score) from 'uncooked' (score 1) to 'tan with no evidence of pink' (score 5). An alternative five point score chart (TCC-score) including texture of the meat, clarity of meat juice and internal colour was also developed. Enumeration of viable E. coli O157:H7gfp+ in cooked hamburgers was based on fluorescent colonies recovered from plates. Results showed that MAP hamburgers developed PMB when compared with controls (P = 0.0003) and that the shortest cooking time for the highest C-score was 6 and 11 min for MAP and control hamburgers, respectively. The mean temperature in the MAP hamburger was then 60.3 degrees C. The TCC-score reduced the difference between MAP and control hamburgers. It was also shown that the survival of E. coli O157:H7gfp+ was highest in MAP hamburgers. The predicted absolute risks for illness were highest for MAP hamburgers for all C-scores and the relative risk associated with PMB increased with doneness. For a C-score of 4 (slightly pink) the predicted relative risk for illness was 300 times higher for MAP hamburger than for controls. A variable pathogen reduction was observed when cooking hamburgers to temperatures of 70-76 degrees C (the 5th and 95th percentile range was around 33 log CFU). The lower reductions, at the 5th percentile, may, depending on initial contamination levels, not be enough to ensure sufficient and safe inactivation of E. coli O157:H7. Efforts to inform consumers about PMB in minced meat packaged in high oxygen packages (>= 60% O-2) are needed with the aim to make consumers use thermometers correctly or at least not determine doneness based only on meat colour. (C) 2015 Elsevier B.V. All rights reserved.
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29.
  • Egervärn, Maria, et al. (författare)
  • Escherichia coli with extended-spectrum beta-lactamases or transferable AmpC beta-lactamases and Salmonella on meat imported into Sweden
  • 2014
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 171, s. 8-14
  • Tidskriftsartikel (refereegranskat)abstract
    • The presence of Enterobacteriaceae producing extended spectrum beta-lactamases (ESBL) or transferable AmpC beta-lactamases (pAmpC) is increasingly being reported in humans and animals world-wide. Their occurrence in food-producing animals suggests that meat is a possible link between the two populations. This study investigated the occurrence and characteristics of Salmonella and ESBL- or pAmpC-producing E. coli in 430 samples of beef, pork and broiler meat imported into Sweden, in order to provide data required for assessing the potential public health risk of these bacteria in food. Depending on region of origin, ESBL/pAmpC-producing E. coli were found in 0-8% of beef samples, 2-13% of pork samples and 15-95% of broiler meat samples. The highest prevalence was in South American broiler meat (95%), followed by broiler meat from Europe (excluding Denmark) (61%) and from Denmark (15%). Isolates from meat outside Scandinavia were generally defined as multiresistant. A majority of the ESBL/pAmpC genes were transferable by conjugation. Bla(CTX-M-2) and bla(CTX-M-8) were the dominant genes in E. coli from South American broiler meat, whereas bla(CMY-2) and bla(CTX-M-1) dominated in European meat. The majority of bla(CMY-2) and bla(CTX-M-1) were situated on plasmids of replicon type incK and incI1, respectively. The same combinations of ESBL/pAmpC genes and plasmids have been described previously in clinical human isolates. Salmonella was found in five samples tested, from European pork and broiler meat. No Salmonella isolate was resistant to third-generation cephalosporins. In conclusion, meat imported into Sweden, broiler meat in particular, is a potential source of human exposure to ESBL- and pAmpC-producing E. coli.
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30.
  • Eriksson, John, et al. (författare)
  • Comparison of genotyping methods by application to Salmonella livingstone strains associated with an outbreak of human salmonellosis
  • 2005
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 104:1, s. 93-103
  • Tidskriftsartikel (refereegranskat)abstract
    • During 2000 and 2001, an outbreak of human salmonellosis occurred in Sweden and Norway, caused by Salmonella livingstone. In this study, the genotypic differences between three strains obtained from food sources during the outbreak, two human strains and 27 more or less unrelated strains were analysed, using the three methods; automated ribotyping, pulsed field get electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD). Each method was evaluated regarding its discriminatory ability, reproducibility and typeability. Simpson's discriminatory index calculated for each method was 0.556 for automated ribotyping, 0.766 for PFGE and 0.236 for RAPD. The reproducibility, defined as the minimum similarity between individual replicates in a cluster analysis, was 96% for automated ribotyping and PFGE, and 90% for RAPD. All the strains were typeable with each method. When combining results for the three genotyping methods, it was found that RAPD did not increase the discriminatory index and was therefore excluded from further analysis. Using a combination of the results obtained from ribotyping and PFGE (D = 0.855), two strains that had been isolated from feed factories during 1998 were shown to be identical to the outbreak strain, indicating a possible route of contamination due to a clone of Salmonella livingstone persisting in feed producing facilities. No connection to poultry was established. (c) 2005 Elsevier B.V. All rights reserved.
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31.
  • Feng, X. M., et al. (författare)
  • Growth of lactic acid bacteria and Rhizopus oligosporus during barley tempeh fermentation
  • 2005
  • Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 104:3, s. 249-256
  • Tidskriftsartikel (refereegranskat)abstract
    • The zygomycete Rhizopus oligosporus is traditionally used to ferment soybean tempeh, but it is also possible to ferment other legumes and cereals to tempeh, The traditional soybean tempeh harbours a multitude of microorganisms with potentially beneficial or detrimental effects on quality. Lactic acid bacteria (LAB) have positive effects on the safety of soybean tempeh, but the effects of LAB on R. oligosporus growth have not been investigated. We have developed a cereal grain tempeh by fermenting pearled barley with R. oligosporus ATCC 64063. Four LAB species, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus reuteri and Lactococcus lactis were assessed for their growth abilities and their effects on R. oligosporus growth during barley tempeh fermentation. Growth of LAB was assayed as colony forming units (cfu), while growth of R. oligosporus was measured as ergosterol content and hyphal length. The two fungal measurements highly correlated (r=0.83, P < 0.001, n = 90). The ergosterol content of fungal mycelia ranged from 11.7 to 30.1 mg/g fungal dry matter. L. plantarum multiplied from 4.8 to 7.4 log cfu/g dry tempeh and L. fermentum increased from 4.4 to 6.8 log cfu/g during 24 h incubation at 35 degrees C. L. reuteri and L. lactis had significantly slower growth, with increases from 4.8 to 5.6 log cfu/g and 5.0 to 5.4 log cfu/g, respectively. The growth of R. oligosporus and the final pH (4.9) in barley tempeh were not significantly influenced by any of the LAB investigated.
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32.
  • Feng, Xin Mei, et al. (författare)
  • Production of volatile compounds by Rhizopus oligosporus during soybean and barley tempeh fermentation
  • 2007
  • Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 113:2, s. 133-141
  • Tidskriftsartikel (refereegranskat)abstract
    • Rhizopus oligosporus Saito can ferment soybeans or cereal grains to tempeh, a sliceable cake with improved nutritional properties. Volatiles produced by different R. oligosporus strains grown on malt extract agar (MEA), barley and soybean were investigated. The effect of co-cultivation with Lactobacillus plantarum on the production of volatiles was also studied. Volatile compounds were collected in situ by headspace diffusion and identified by GC-MS. The ten R. oligosporus strains that had different colony morphologies on MEA produced very similar volatile profiles, except for slight variations among the minor volatile compounds (e.g. sesquiterpenes). Likewise, practically no differences in volatile profiles were observed between three of the strains grown on soybeans. In contrast, the R. oligosporus volatile profile on soybean was different from that on barley from the same strain. Co-cultivation with L. plantarum did not influence volatile production by R. oligosporus. The dominant compounds produced on all three Substrates were ethanol, acetone, ethyl acetate, 2-butanone, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Acetaldehyde and 2-methyl-propanal were also produced on MEA and barley, while 2-pentanone, methyl acetate, 2-butanol and 3-methyl-3-buten-1-ol were observed on soybeans. Ethanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most abundant volatile compounds produced on MEA and barley, while 2-butanone was the dominant volatile metabolite on soybean. The mushroom odour compounds, 3-octanone and 1-octen-3-ol, were only detected from soybean and soybean tempeh.
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33.
  • Grønlund, H., et al. (författare)
  • Microarray-based genotyping of Salmonella : Inter-laboratory evaluation of reproducibility and standardization potential
  • 2011
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 145:SUPPL. 1, s. S79-S85
  • Tidskriftsartikel (refereegranskat)abstract
    • Bacterial food-borne infections in humans caused by Salmonella spp. are considered a crucial food safety issue. Therefore, it is important for the risk assessments of Salmonella to consider the genomic variation among different isolates in order to control pathogen-induced infections. Microarray technology is a promising diagnostic tool that provides genomic information on many genes simultaneously. However, standardization of DNA microarray analysis is needed before it can be used as a routine method for characterizing Salmonella isolates across borders and laboratories. A comparative study was designed in which the agreement of data from a DNA microarray assay used for typing Salmonella spp. between two different labs was assessed. The study was expected to reveal the possibility of obtaining the same results in different labs using different equipment in order to evaluate the reproducibility of the microarray technique as a first step towards standardization. The low-density array contains 281 57-60-mer oligonucleotide probes for detecting a wide range of specific genomic marker genes associated with antibiotic resistance, cell envelope structures, mobile genetic elements and pathogenicity. Several critical methodology parameters that differed between the two labs were identified. These related to printing facilities, choice of hybridization buffer, wash buffers used following the hybridization and choice of procedure for purifying genomic DNA. Critical parameters were randomized in a four-factorial experiment and statistical measures of inter-lab consistency and agreement were performed based on the kappa coefficient. A high level of agreement (kappa = 0.7-1.0) in microarray results was obtained even when employing different printing and hybridization facilities, different procedures for purifying genomic DNA and different wash buffers. However, less agreement (Kappa = 0.2-0.6) between microarray results were observed when using different hybridization buffers, indicating this parameter as being highly critical when transferring a standard microarray assay between laboratories. In conclusion, this study indicates that DNA microarray assays can be reproduced in at least two different facilities, which is a pre-requisite for the development of standard guidelines. © 2010 Elsevier B.V.
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34.
  • Guo, Zhiming, et al. (författare)
  • Label-free surface enhanced Raman scattering spectroscopy for discrimination and detection of dominant apple spoilage fungus
  • 2021
  • Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 338
  • Tidskriftsartikel (refereegranskat)abstract
    • Fungal infection is one of the main causes of apple corruption. The main dominant spoilage fungi in causing apple spoilage are storage mainly include Penicillium Paecilomyces paecilomyces (P. paecilomyces), penicillium chrysanthemum (P. chrysogenum), expanded Penicillium expansum (P. expansum), Aspergillus niger (Asp. niger) and Alternaria. In this study, surface-enhanced Raman spectroscopy (SERS) based on gold nanorod (AuNRs) substrate method was developed to collect and examine the Raman fingerprints of dominant apple spoilage fungus spores. Standard normal variable (SNV) was used to pretreat the obtained spectra to improve signal-tonoise ratio. Principal component analysis (PCA) was applied to extract useful spectral information. Linear discriminant analysis (LDA) and non-linear pattern recognition methods including K nearest neighbor (KNN), Support vector machine (SVM) and back propagation artificial neural networks (BPANN) were used to identify fungal species. As the comparison of modeling results shown, the BPANN model established based on the characteristic spectra variables have achieved the satisfactory result with discrimination accuracy of 98.23%; while the PCA-LDA model built using principal component variables achieved the best distinguish result with discrimination accuracy of 98.31%. It was concluded that SERS has the potential to be an inexpensive, rapid and effective method to detect and identify fungal species.
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35.
  • Haros, Monica, et al. (författare)
  • Phytate degradation by human gut isolated Bifidobacterium pseudocatenulatum ATCC27919 and its probiotic potential
  • 2009
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 135:1, s. 7-14
  • Tidskriftsartikel (refereegranskat)abstract
    • The growing awareness of the relationship between diet and health has led to an increasing demand for food products that support health above and beyond providing basic nutrition. Probiotics are live organisms present in foods, which yield health benefits related to their interactions with the gastrointestinal tract. Phytases are a subgroup of phosphatases that catalyse the desphosphorylation of phytate, which reduces its negative impact on mineral bioavailability, and generates lower inositol phosphates. The aims of this investigation were to (i) study the ability of the probiotic candidate Bifidobacterium pseudocatenulatum to degrade phytate in synthetic medium, to (ii) identify the lower inositol phosphates generated, to (iii) study its survival under conditions mimicking gastrointestinal passage and finally to (iv) assess adhesion of the bacteria to Caco-2 cells. The first steps of InsP(6) degradation by B. pseudocatenulatum phytate-degrading enzyme/s were preferentially initiated at the DL-6-position and 5-position of the myo-inositol ring. It suggests that the main InsP(6) degradation pathway by B. pseudocatenulatum by sequential removal of phosphate groups was D/L-Ins(1,2,3,4,5)P(5) or D/L-Ins(1,2,3,4,6)P(5); D/L-Ins(1,2,3,4)P(4); to finally Ins(1,2,3)P(3) and D/L-Ins(1,2,4)P(3)/D/L-Ins(1,3,4)P(3). This human strain also showed a notable tolerance to bile as well as a selective adhesion capacity (adhesion to control surfaces was zero), to human intestinal Caco-2 cells comparable to the commercial probiotic B. lactis. The phytate-degrading activity constitutes a novel metabolic trait which could contribute to the improvement of mineral absorption in the intestine as a nutritional probiotic feature with potential trophic effect in human gut.
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36.
  • Hedell, Ronny, 1985, et al. (författare)
  • Detection probability models for bacteria, and how to obtain them from heterogeneous spiking data. An application to Bacillus anthracis
  • 2017
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 241, s. 78-88
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2016 Elsevier B.V.Efficient and correct evaluation of sampling results with respect to hypotheses about the concentration or distribution of bacteria generally requires knowledge about the performance of the detection method. To assess the sensitivity of the detection method an experiment is usually performed where the target matrix is spiked (i.e. artificially contaminated) with different concentrations of the bacteria, followed by analyses of the samples using the pre-enrichment method and the analytical detection method of interest. For safety reasons or because of economic or time limits it is not always possible to perform exactly such an experiment, with the desired number of samples. In this paper, we show how heterogeneous data from diverse sources may be combined within a single model to obtain not only estimates of detection probabilities, but also, crucially, uncertainty estimates. We indicate how such results can then be used to obtain optimal conclusions about presence of bacteria, and illustrate how strongly the sampling results speak in favour of or against contamination. In our example, we consider the case when B. cereus is used as surrogate for B. anthracis, for safety reasons. The statistical modelling of the detection probabilities and of the growth characteristics of the bacteria types is based on data from four experiments where different matrices of food were spiked with B. anthracis or B. cereus and analysed using plate counts and qPCR. We show how flexible and complex Bayesian models, together with inference tools such as OpenBUGS, can be used to merge information about detection probability curves. Two different modelling approaches, differing in whether the pre-enrichment step and the PCR detection step are modelled separately or together, are applied. The relative importance on the detection curves for various existing data sets are evaluated and illustrated.
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37.
  • Hellström, Andreas, 1980, et al. (författare)
  • Biodiversity and phytase capacity of yeasts isolated from Tanzanian togwa
  • 2010
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 136:3, s. 352-358
  • Tidskriftsartikel (refereegranskat)abstract
    • The focus of the present investigation was on the Tanzanian fermented food togwa as a source for dietary iron and zinc, and the potential for mineral availability improvements using selected yeasts. To establish the content of target minerals and main inhibitor for intestinal uptake, iron and zinc as well as the mineral chelating phytic acid, (IP6 or phytate) were determined in naturally fermented togwa. Yeasts were isolated from sorghum, maize and cassava based togwa, and identified by sequencing the D1/D2 region of the LSU rRNA gene. The isolated yeasts were subsequently screened for phytase activity.The total iron content in sorghum, maize and cassava based togwa were 41.5 (±7.2), 85.4 (±31.9) and 28.6 (±3.8) μg/g dw (dry weight) respectively. The zinc content was 12.3 (±3.1), 11.0 (±1.1) and 6.4 (±4.5) μg/g dw in sorghum, maize and cassava based togwa, and the phytate content in the three varieties were 2.6±1.2, 4.7±0.8 and 0.4±0.4 μmol/g dw respectively. The phytate levels in the sorghum and maize based togwa are expected to substantially reduce the availability of iron. The molar ratio phytate to iron for these two varieties were estimated to be 3.5:1 and 3.1:1 respectively. In general, a phytate to iron molar ratio below 1 is needed to increase the availability of iron.Among 26 isolates, 9 different species could be distinguished: Issatchenkia orientalis, Pichia anomala, Pichia norvegensis, Pichia burtonii, Pichia guilliermondii, Kluyveromyces marxianus, Saccharomyces cerevisiae, Hanseniaspora guilliermondii and Candida glabrata. The strains were screened for phytase activity in YPD supplemented with 0.5 mM IP6. Of 26 screened strains, the phytase activity was most prominent in strains of I. orientalis and H. guilliermondii. The strains and data constitute a basis for further improvements of iron andzinc bioavailability in togwa.
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38.
  • Hellström, Andreas, 1980, et al. (författare)
  • Degradation of phytate by Pichia kudriavzevii TY13 and Hanseniaspora guilliermondii TY14 in Tanzanian togwa
  • 2012
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 153:1-2, s. 73-77
  • Tidskriftsartikel (refereegranskat)abstract
    • The fermented cereal-based gruel togwa is used as weaning food for children in Tanzania. Togwa is rich in minerals but these are often not available for uptake in the human intestine due to natural inhibitors, such as phytate (IP 6). The yeasts Pichia kudriavzevii TY13, Hanseniaspora guilliermondii TY14 and TY20, isolated from Tanzanian togwa, and selected for high phytase activity in complex yeast medium YPD, were now studied regarding their ability to degrade IP 6 in maize-based model togwa. A modified constitutively high-phytase producing Saccharomyces cerevisiae BY80 and commercial Aspergillus ficuum phytase were included for comparison. In addition, a strain of Lactobacillus plantarum was included in the model-togwa set-up.All yeasts in the study grew and reached final cell density 1.5-2 log units higher than the start value. S. cerevisiae BY80 degraded 85% of the IP 6 in 48h; the same degradation level as with A. ficuum phytase (89%). Of the togwa-isolated yeasts, P. kudriavzevii TY13 and H. guilliermondii TY14 showed strong phytate degradation in the model-togwa; 95% or more of the initial IP 6 was degraded after 48h. This corresponds to a remaining level of 0.4 and 0.3μmol IP 6/g dw. Co-inoculation with L. plantarum did not increase IP 6 degradation. Moreover, fermentation with P. kudriavzevii TY13 yielded a successive increase in inorganic phosphate (P i), from 0.7 to 5.4mM, suggesting a phytase production in TY13 which is fairly insensitive to P i repression. The study shows that phytate in a model togwa is available for yeast phytase enzymes, and addresses the importance of strain selection for effectively degrading the phytate. Certain yeasts originating from togwa seem to have developed a natural high phytase production, and P. kudriavzevii TY13 and H. guilliermondii TY14 seem particularly well adapted to phytate degradation in togwa, and is our choice for further studies and strain improvement.
  •  
39.
  • Hernroth, Bodil, 1951, et al. (författare)
  • The persistence of infectious adenovirus (type 35) in mussels (Mytilus edulis) and oysters (Ostrea edulis)
  • 2007
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 113:3, s. 296-302
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to provide information for improving risk assessment of viral contaminants in bivalves. The persistence of viable adenovirus type 35 (Ad35) after controlled contaminations of blue mussels, Mytilus edulis, and oysters, Ostrea edulis, was studied. Bivalves, kept in running seawater at two different temperatures (4 and 18 degrees C) were sampled after 1, 3, 7, 14, 21, 35, 42, 49, 56, and 70 days. Virus particles were separated from the gills and the digestive gland through ultra high-speed centrifugation. Qualitative PCR analyses of DNA in the virus extracts showed that Ad35 was detectable for 6-10 weeks and quantitative real-time PCR verified a gradual but not linear decrease in copy numbers, within this time interval. The virus genome was detectable to the same degree on the gills as in the digestive gland. When viral extractions were inoculated on A549 cells to investigate the cytopathic effect (CPE) it was shown that Ad35 stayed infectious in oysters, kept at 4 degrees, for about six weeks, which was double the time compared to that for mussels. The detection of the viral genome exceeded the persistence of their infectivity, in most cases with 4-6 weeks. The data were highly variable and the sporadic occurrence of high numbers of accumulated viruses and their remaining infectivity is seemingly a significant factor regarding food safety. (c) 2006 Elsevier B.V. All rights reserved.
  •  
40.
  • Hjortmo, Sofia, 1978, et al. (författare)
  • Biofortification of folates in white wheat bread by selection of yeast strain and process
  • 2008
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 127:1-2, s. 32-36
  • Tidskriftsartikel (refereegranskat)abstract
    • We here demonstrate that folate content in yeast fermented food can be dramatically increased by using a proper (i) yeast strain and (ii) cultivation procedure for the selected strain prior to food fermentation. Folate levels were 3 to 5-fold higher in white wheat bread leavened with a Saccharomyces cerevisiae strain CBS7764, cultured in defined medium and harvested in the respiro-fermentative phase of growth prior to dough preparation (135-139 mu g/100 dry matter), compared to white wheat bread leavened with commercial Baker's yeast (27-43 mu g/100 g). The commercial Baker's yeast strain had been industrially produced, using a fedbatch process. thereafter compressed and stored in the refrigerator until bakings were initiated. This strategy is an attractive alternative to fortification of bread with synthetically produced folic acid. By using a high folate producing strain cultured a suitable way folate levels obtained were in accordance with folic acid content in fortified cereal products.
  •  
41.
  • Hjortmo, Sofia, 1978, et al. (författare)
  • Growth rate and medium composition strongly affect folate content in Saccharomyces cerevisiae
  • 2008
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 123:1-2, s. 93-100
  • Tidskriftsartikel (refereegranskat)abstract
    • Folate content in a Saccharomyces cerevisiae strain was monitored during aerobic batch fermentation in synthetic growth medium, yeast peptone dextrose medium, and a molasses based medium. During growth in the synthetic medium large differences in intracellular folate content was observed at different phases. Specific folate levels, expressed per unit biomass, were highest during respiro-fermentative growth (120 mu g/g) and decreased during the respiratory and stationary phases. Thus, the physiological state of the cells clearly affects the folate content. This was confirmed in chemostat Cultures where total intracellular folate content increased linearly with increasing growth rate (r(2) = 0.998), indicating high growth rate i.e. respiro-fermentative growth to be most favourable to obtain high specific folate content. In complex media however, much lower folate content (15-40 mu g/g) was found throughout the batch growth. Only minor growth-phase related differences were detected. This shows the impact of cultivation medium on folate content in yeast. To further investigate which components that influence folate content, batch experiments in synthetic medium with addition of specific components were performed. Adding a raw mixture of peptides and amino acids (peptone) decreased folate levels extensively (90%) whereas adding amino acids one-by-one only had minor effects on the intracellular folate content. Furthermore, supplementing synthetic medium with pABA, folate or nucleotides did not change the intracellular folate content. This work constitutes the first steps towards an optimised process for production of natural folates for fortification Purposes, as well as an effort to gain fundamental understanding of folate requirements in yeast in relation to environmental conditions.
  •  
42.
  • Jacobson, Magdalena, et al. (författare)
  • Flotation—A New Method to Circumvent PCR Inhibitors in the Diagnosis of Lawsonia intracellularis
  • 2009
  • Ingår i: International Journal of Food Microbiology. - : Hindawi Limited. - 0168-1605 .- 1879-3460 .- 1687-918X .- 1687-9198. ; 2009
  • Tidskriftsartikel (refereegranskat)abstract
    • The obligate intracellular bacteriumLawsonia intracellulariscauses enteritis and poor growth in weaned pigs. Cultivation is difficult and diagnosisante mortemis mainly based on techniques such as polymerase chain reaction. However, false negative results caused by the presence of PCR-inhibitory factors constitute a problem. This study aimed to develop and evaluate a new technique, flotation, to separateL. intracellularisfrom inhibitors in faeces prior to PCR. The technique was evaluated by comparison to two previously evaluated and commonly used methods, preparation by boiling lysate combined with nested PCR and preparation by a commercial kit combined with conventional PCR. Continuous density centrifugation of faecal samples containingL. intracellularissuggested the buoyant density of the microbe to be between 1.064 and 1.077 g/mL. Several flotation setups were tested to achieve optimal separation of the microbe from inhibitors and faecal particles. The finally selected setup floated wholeL. intracellularisfrom the application site at the bottom to the upper part of the gradient while inhibitory components mainly remained in the bottom. PCR was performed directly on material recovered from the upper interphase. The method was evaluated on 116 clinical samples. As compared to sample preparation by boiling combined with nested PCR, fewer samples were inhibited but also fewer positives were identified. In comparison to preparation by a commercial kit combined with conventional PCR, presently used for routine diagnosis, similar results were obtained. However, the new method was comparably faster to perform. The new method, based on flotation ofLawsonia intracellulariscombined with conventional PCR, was well suited for routine diagnosis.
  •  
43.
  • Jensen, Dan Funck (författare)
  • Characterization of microbial communities and fungal metabolites on field grown strawberries from organic and conventional production
  • 2013
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 160, s. 313-322
  • Tidskriftsartikel (refereegranskat)abstract
    • The background levels of culturable indigenous microbial communities (microbiotas) on strawberries were examined in a field survey with four conventional and four organic growers with different production practise and geographic distribution. The microbiota on apparently healthy strawberries was complex including potential plant pathogens, opportunistic human pathogens, plant disease biocontrol agents and mycotoxin producers. The latter group was dominated by Penicillium spp. and Aspergillus niger was also isolated. As expected, bacteria were the most abundant and diverse group of the strawberry microbiota followed by yeasts and filamentous fungi. No obvious correlation between grower practice and the strawberry microbiota was observed. Differences between microbiotas on strawberries from conventional systems with up to 10 fungicide spray treatments and organic production systems were insignificant. Mycotoxins were not detected in mature strawberries from any of the eight different growers neither in additional samples of low quality berries. However, isolates of Penicillium expansum and A. niger produced high amounts of mycotoxins when incubated on strawberries at 25 degrees C. Penicillium polonicum produced cyclopenol, cyclopenin, and viridicatin on the artificially infected berries, while Altemaria arborescens produced tenuazonic acid, Alternaria tenuissima produced altertoxin land altenuene, and Trichoderma spp. produced several peptaibols. In conclusion, native strawberry microbiotas are highly diverse both in terms of taxonomic groups and functional traits that are important in relation to plant and human health. (C) 2012 Elsevier B.V. All rights reserved.
  •  
44.
  • Karlsson, Ida, et al. (författare)
  • Agricultural factors affecting Fusarium communities in wheat kernels
  • 2017
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 252, s. 53-60
  • Tidskriftsartikel (refereegranskat)abstract
    • Fusarium head blight (FHB) is a devastating disease of cereals caused by Fusarium fungi. The disease is of great economic importance especially owing to reduced grain quality due to contamination by a range of mycotoxins produced by Fusarium. Disease control and prediction is difficult because of the many Fusarium species associated with FHB. Different species may respond differently to control methods and can have both competitive and synergistic interactions. Therefore, it is important to understand how agricultural practices affect Fusarium at the community level.Lower levels of Fusariwn mycotoxin contamination of organically produced cereals compared with conventionally produced have been reported, but the causes of these differences are not well understood. The aim of our study was to investigate the effect of agricultural factors on Fusarium abundance and community composition in different cropping systems. Winter wheat kernels were collected from 18 organically and conventionally cultivated fields in Sweden, paired based on their geographical distance and the wheat cultivar grown. We characterised the Fusarium community in harvested wheat kernels using 454 sequencing of translation elongation factor 1-alpha amplicons. In addition, we quantified Fusariwn spp. using real-time PCR to reveal differences in biomass between fields.We identified 12 Fusariwn operational taxonomic units (OTUs) with a median of 4.5 OTUs per field. Fusarium graminearum was the most abundant species, while F. avenaceum had the highest occurrence. The abundance of Fusariwn spp. ranged two orders of magnitude between fields. Two pairs of Fusariurt species co-occurred between fields: F. poae with F. tricinctwn and F. culmorwn with F. sporofrichoides. We could not detect any difference in Fusariwn communities between the organic and conventional systems. However, agricultural intensity, measured as the number of pesticide applications and the amount of nitrogen fertiliser applied, had an impact on Fusariwn communities, specifically increasing the abundance of F. tricinctwn. There were geographical differences in the Fusarium community composition where F. graminearwn was more abundant in the western part of Sweden. The application of amplicon sequencing provided a comprehensive view of the Fusarium community in cereals. This gives us better opportunities to understand the ecology of Fusarium spp., which is important in order to limit FHB and mycotoxin contamination in cereals.
  •  
45.
  • Knutsson, R., et al. (författare)
  • Accidental and deliberate microbiological contamination in the feed and food chains - How biotraceability may improve the response to bioterrorism
  • 2011
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 145:SUPPL. 1, s. S123-S128
  • Tidskriftsartikel (refereegranskat)abstract
    • A next frontier of the global food safety agenda has to consider a broad spectrum of bio-risks, such as accidental and intentional contaminations in the food and feed chain. In this article, the background for the research needs related to biotraceability and response to bioterrorism incidents are outlined. Given the current scale of international trade any response need to be considered in an international context. Biotraceability (e.g. the ability to use downstream information to point to processes or within a particular food chain that can be identified as the source of undesirable agents) is crucial in any food-born outbreak and particular in the response to bioterrorism events. In the later case, tested and proven biotraceability improves the following: (i) international collaboration of validated tracing tools and detection methods, (ii) multi-disciplinary expertise and collaboration in the field of food microbiology and conceptual modeling of the food chain, (iii) sampling as a key step in biotracing (iv) optimized sample preparation procedures, including laboratory work in Biosafety level 3 (BSL-3) laboratories, (v) biomarker discovery for relevant tracing and tracking applications, and (vi) high-throughput sequencing using bio-informatic platforms to speed up the characterization of the biological agent. By applying biotraceability, the response phase during a bioterrorism event may be shortened and is facilitated for tracing the origin of biological agent contamination. © 2010 Elsevier B.V.
  •  
46.
  • Kolseth, Anna-Karin (författare)
  • Draft genome sequence and chemical profiling of Fusarium langsethiae, an emerging producer of type A trichothecenes
  • 2016
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 221, s. 29-36
  • Tidskriftsartikel (refereegranskat)abstract
    • Fusarium langsethiae is a widespread pathogen of small grain cereals, causing problems with T-2 and HT-2 toxin contamination in grains every year. In an effort to better understand the biology of this fungus, we present a draft genome sequence of F. langsethiae Fl201059 isolated from oats in Norway. The assembly was fragmented, but reveals a genome of approximately 37.5 Mb, with a GC content around 48%, and 12,232 predicted protein-coding genes. Focusing on secondary metabolism we identified candidate genes for 12 polyketide synthases, 13 non ribosomal peptide synthetases, and 22 genes for terpene/isoprenoid biosynthesis. Some of these were found to be unique compared to sequence databases. The identified putative Tri5 cluster was highly syntenic to the cluster reported in F. sporotrichioides. Fusarium langsethiae Fl201059 produces a high number of secondary metabolites on Yeast Extract Sucrose (YES) agar medium, dominated by type A trichothecenes. Interestingly we found production of glucosylated HT-2 toxin (Glu-HT-2), previously suggested to be formed by the host plant and not by the fungus itself. In greenhouse inoculations of F. langsethiae FI201059 on barley and oats, we detected the type A trichothecenes: neosolaniol, HT-2 toxin, T-2 toxin, Glu-HT-2 and numerous derivatives of these. (C) 2016 Elsevier B.V. All rights reserved.
  •  
47.
  • Krämer, N., et al. (författare)
  • A novel strategy to obtain quantitative data for modelling : Combined enrichment and real-time PCR for enumeration of salmonellae from pig carcasses
  • 2011
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 145:SUPPL. 1, s. S86-S95
  • Tidskriftsartikel (refereegranskat)abstract
    • Salmonella is a major zoonotic pathogen which causes outbreaks and sporadic cases of gastroenteritis in humans worldwide. The primary sources for Salmonella are food-producing animals such as pigs and poultry. For risk assessment and hazard analysis and critical control point (HACCP) concepts, it is essential to produce large amounts of quantitative data, which is currently not achievable with the standard cultural based methods for enumeration of Salmonella. This study presents the development of a novel strategy to enumerate low numbers of Salmonella in cork borer samples taken from pig carcasses as a first concept and proof of principle for a new sensitive and rapid quantification method based on combined enrichment and real-time PCR. The novelty of the approach is in the short pre-enrichment step, where for most bacteria, growth is in the log phase. The method consists of an 8h pre-enrichment of the cork borer sample diluted 1:10 in non-selective buffered peptone water, followed by DNA extraction, and Salmonella detection and quantification by real-time PCR. The limit of quantification was 1.4 colony forming units (CFU)/20cm2 (approximately 10g) of artificially contaminated sample with 95% confidence interval of±0.7 log CFU/sample. The precision was similar to the standard reference most probable number (MPN) method. A screening of 200 potentially naturally contaminated cork borer samples obtained over seven weeks in a slaughterhouse resulted in 25 Salmonella-positive samples. The analysis of salmonellae within these samples showed that the PCR method had a higher sensitivity for samples with a low contamination level (<6.7CFU/sample), where 15 of the samples negative with the MPN method was detected with the PCR method and 5 were found to be negative by both methods. For the samples with a higher contamination level (6.7-310CFU/sample) a good agreement between the results obtained with the PCR and MPN methods was obtained. The quantitative real-time PCR method can easily be applied to other food and environmental matrices by adaptation of the pre-enrichment time and media. © 2010 Elsevier B.V.
  •  
48.
  • Kure, C.F., et al. (författare)
  • Use of the selective agar medium CREAD for monitoring the level of airborne spoilage moulds in cheese production
  • 2008
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 122:42006, s. 29-34
  • Tidskriftsartikel (refereegranskat)abstract
    • It was investigated if a selective medium for common cheese spoiling moulds (CREAD) could give more relevant information than a general mould medium in hygienic air-sampling in cheese factories. A total of 126 air-samples were taken in six Nordic cheese factories using the general mould medium DG18 and CREAD. The level and genera of air-borne mould was determined. Identification to species-level was performed for a selection of samples. In five cheese factories the mycobiota was dominated by Penicillium spp. and in one cheese factory by Cladosporium spp. The concentration of air-borne moulds varied between the cheese factories ranging from 1 to 270 cfu/m3 on DG18 with a median value of 17. The number of mould colonies was in general lower at CREAD. Identification indicated that CREAD supported growth of common spoilage moulds for cheese, such as Penicillium palitans and P. commune. The mycobiota on DG18 also consisted of moulds not commonly associated with spoilage of cheese, such as Cladosporium spp., P. brevicompactum and P. chrysogenum. Contamination of cheese with mould is periodically a problem in production of semi-hard cheese and the level of air-borne mould is therefore routinely monitored in cheese factories. A clear correlation between the total number of moulds in air and mould growth on products is not always found. The conclusion from the investigation is that it is recommended to use a selective medium for cheese spoilage moulds, such as CREAD in hygienic monitoring. © 2007 Elsevier B.V. All rights reserved.
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49.
  • Le Guyader, Francoise S, et al. (författare)
  • Detection of noroviruses in raspberries associated with a gastroenteritis outbreak
  • 2004
  • Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 97:2, s. 179-186
  • Tidskriftsartikel (refereegranskat)abstract
    • Following an acute foodborne gastroenteritis outbreak in southern Sweden, stool specimens from five of nine ill patients were found positive for norovirus using reverse transcriptase polymerase chain reaction. Epidemiological data pointed to raspberry cakes as the source of the outbreak. Using a combination of generic and patient-specific primers and novel food analysis methodology (with extraction efficiency control and inhibitor removal), norovirus strains from two different genogroups were directly identified in the contaminated raspberries.
  •  
50.
  • Leong, Su-lin L., et al. (författare)
  • The extreme xerophilic mould Xeromyces bisporus : Growth and competition at various water activities
  • 2011
  • Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 145:1, s. 57-63
  • Tidskriftsartikel (refereegranskat)abstract
    • Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (a(w)) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X. bisporus were assessed at 20, 25, 30 and 37 degrees C on solid agar media containing a mixture of glucose and fructose to reduce a(w) to 0.94, 0.88, 0.84, 0.80, 0.76 and 0.66. Growth rates of xerophilic species closely related to X. bisporus, viz. Chrysosporium Mops, C. xerophilum and Monascus eremophilus, were also assessed. Optimal conditions for growth of both X. bisporus strains were approx. 0.84 a(w) and 30 degrees C, despite FRR 2347 growing two- to five-fold faster than CBS 185.75. X. bisporus FRR 2347 even grew well at 0.66 a(w) (0.48 mm/day). C. Mops and C xerophilurn were more tolerant of high a(w) than X. bisporus. and could be differentiated from each other based on: the faster growth of C. xerophilum; its preference for temperatures >= 30 degrees C and a(w) >= 0.94 (c.f. <= 25 degrees C and similar to 0.88 a(w) for C Mops); and its ability to grow at 0.66 a(w), which is the lowest a(w) reported to date for this species. M. eremophilus grew slowly (max. 0.4 mm/day) even in its optimal conditions of similar to 0.88 a(w) and 25 degrees C. To investigate the competitive characteristics of X. bisporus at low a(w), both X. bisporus strains were grown in dual-culture with xerotolerant species Aspergillus flavus and Penicillium roqueforti, and xerophilic species A. penicillioides, C. Mops, C. xerophilum and Eurotium chevalieri, on glucose-fructose agar plates at 0.94, 0.84, 0.80 and 0.76 a(w) and at 25 degrees C. Growth rates and types of interactions were assessed. Excretion of inhibitory substances acting over a long-range was not observed by any species; inhibitors acting over a short-range that temporarily slowed competitors' growth or produced a protective zone around the colony were occasionally observed for A. penicillioides, C. Mops and C. xerophilum. Instead, rapid growth relative to the competitor was the most common means of dominance. The xerotolerant species. A. flavus and P. roqueforti were dominant over X. bisporus at 0.94 a(w). E. chevalieri was often dominant due to its rapid growth over the entire a(w) range. At a(w) < 0.80, X. bisporus was competitive because it grew faster than the other species examined. This supports the concept that its ideal environmental niche is sugary foods with low a(w).
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