| 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. |
- 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.
|
|
| 5. |
- 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.
|
|
| 6. |
- 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.
|
|
| 7. |
|
|
| 8. |
|
|
