| 1. |
- Blixt, Y., et al.
(författare)
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Interlaboratory random amplified polymorphic DNA typing of Yersinia enterocolitica and Y. enterocolitica-like bacteria
- 2003
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 83:1, s. 15-26
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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)
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Prevalence of Clostridium botulinum types B, E, and F in faecal samples from Swedish cattle.
- 2003
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 82:2, s. 105-110
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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)
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Evaluation of selective enrichment PCR procedures for Yersinia enterocolitica.
- 2002
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 73:1, s. 35-46
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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)
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Comparison between automatic ribotyping and random amplified polymorphic DNA analysis of Bacillus cereus isolates from the dairy industry
- 1999
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 47:42006, s. 147-151
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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)
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The adhesion of Bacillus cereus spores to epithelial cells might be an additional virulence mechanism
- 1998
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 39:1-2, s. 93-9
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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)
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Inhibition of Staphylococcus aureus and spheroplasts of Gram-negative bacteria by an antagonistic compound produced by a strain of Lactobacillus plantarum
- 1986
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 3:3, s. 149-160
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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)
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Nitrate reduction during fermentation by Gram-negative bacterial activity in carrots
- 1985
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 2:4, s. 219-225
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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)
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Growth of pulsed electric field exposed Escherichia coli in relation to inactivation and environmental factors
- 2004
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 93:1, s. 1-10
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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)
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Campylobacter incidence on a chicken farm and the spread of Campylobacter during the slaughter process
- 1996
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 32:1-2, s. 35-47
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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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