| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 6. |
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
| 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.
|
|
