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  • 1.
    Andersson, Annika
    et al.
    SIK – Institutet för livsmedel och bioteknik.
    Granum, P.E.
    Rönner, Ulf
    SIK – Institutet för livsmedel och bioteknik.
    The adhesion of Bacillus cereus spores to epithelial cells might be an additional virulence mechanism1998In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 39, no 42006, p. 93-99Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Andersson, Annika
    et al.
    SIK – Institutet för livsmedelsforskning.
    Rönner, Ulf
    SIK – Institutet för livsmedelsforskning.
    Granum, P.E.
    What problems does the food industry have with the spore-forming pathogens Bacillus cereus and Clostridium perfringens?1995In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 28, no 2, p. 145-155Article in journal (Refereed)
  • 3.
    Andersson, Annika
    et al.
    SIK – Institutet för livsmedel och bioteknik.
    Svensson, B.
    Christiansson, A.
    Rönner, Ulf
    SIK – Institutet för livsmedel och bioteknik.
    Comparison between automatic ribotyping and random amplified polymorphic DNA analysis of Bacillus cereus isolates from the dairy industry1999In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 47, no 42006, p. 147-151Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Andersson, Rolf E.
    SIK – Svenska livmedelsinstitutet.
    Inhibition of Staphylococcus aureus and spheroplasts of Gram-negative bacteria by an antagonistic compound produced by a strain of Lactobacillus plantarum1986In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 3, no 3, p. 149-160Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Andersson, Rolf E.
    Nitrate reduction during fermentation by Gram-negative bacterial activity in carrots1985In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 2, no 4, p. 219-225Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Aronsson, Kristina
    et al.
    SIK – Institutet för livsmedel och bioteknik.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Stenlof, B.
    Rönner, Ulf
    SIK – Institutet för livsmedel och bioteknik.
    Growth of pulsed electric field exposed Escherichia coli in relation to inactivation and environmental factors2004In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 93, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Aronsson, Kristina
    et al.
    SIK – Institutet för livsmedel och bioteknik.
    Rönner, Ulf
    SIK – Institutet för livsmedel och bioteknik.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    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 processing2005In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 99, no 1, p. 19-32Article in journal (Refereed)
    Abstract [en]

    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.

  • 8. Blixt, Y.
    et al.
    Knutsson, R.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Radstrom, P.
    Interlaboratory random amplified polymorphic DNA typing of Yersinia enterocolitica and Y. enterocolitica-like bacteria2003In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 83, no 1, p. 15-26Article in journal (Refereed)
    Abstract [en]

    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.

  • 9. Dahlenborg, M.
    et al.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Radstrom, P.
    Prevalence of Clostridium botulinum types B, E and F in faecal samples from Swedish cattle2003In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 82, no 2, p. 105-110Article in journal (Refereed)
    Abstract [en]

    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. © 2002 Elsevier Science B.V. All rights reserved.

  • 10. Eriksson, J.
    et al.
    Lofstrom, C.
    Aspan, A.
    Gunnarsson, A.
    Karlsson, I.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Comparison of genotyping methods by application to Salmonella livingstone strains associated with an outbreak of human salmonellosis2005In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 104, no 1, p. 93-103Article in journal (Refereed)
    Abstract [en]

    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 gel 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. © 2005 Elsevier B.V. All rights reserved.

  • 11. Grønlund, H.
    et al.
    Riber, L.
    Vigre, H.
    Löfström, Charlotta
    DTU Technical University of Denmark, Denmark.
    Folling, L.
    Huehn, S.
    Malorny, B.
    Rådström, P.
    Rudi, K.
    Hoorfar, J.
    Microarray-based genotyping of Salmonella: Inter-laboratory evaluation of reproducibility and standardization potential2011In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no SUPPL. 1, p. S79-S85Article in journal (Refereed)
    Abstract [en]

    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.

  • 12. Knutsson, R.
    et al.
    Blixt, Y.
    Grage, H.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Radstrom, P.
    Evaluation of selective enrichment PCR procedures for Yersinia enterocolitica2002In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 73, no 1, p. 35-46Article in journal (Refereed)
    Abstract [en]

    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 °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 °C, followed by Percoll density centrifugation, and a 100 times dilution prior to PCR analysis. © 2002 Elsevier Science B.V. All rights reserved.

  • 13. Knutsson, R.
    et al.
    van Rotterdam, B.
    Fach, P.
    De Medici, D.
    Fricker, M.
    Löfström, Charlotta
    DTU Technical University of Denmark, Denmark.
    Ågren, J.
    Segerman, B.
    Andersson, G.
    Wielinga, P.
    Fenicia, L.
    Skiby, J.
    Schultz, A. C.
    Ehling-Schulz, M.
    Accidental and deliberate microbiological contamination in the feed and food chains - How biotraceability may improve the response to bioterrorism2011In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no SUPPL. 1, p. S123-S128Article in journal (Refereed)
    Abstract [en]

    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.

  • 14. Krämer, N.
    et al.
    Löfström, Charlotta
    DTU Technical University of Denmark, Denmark.
    Vigre, H.
    Hoorfar, J.
    Bunge, C.
    Malorny, B.
    A novel strategy to obtain quantitative data for modelling: Combined enrichment and real-time PCR for enumeration of salmonellae from pig carcasses2011In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no SUPPL. 1, p. S86-S95Article in journal (Refereed)
    Abstract [en]

    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.

  • 15. Kure, C.F.
    et al.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Karlsson, I.
    Homleid, J.P.
    Langsrud, S.
    Use of the selective agar medium CREAD for monitoring the level of airborne spoilage moulds in cheese production2008In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 122, no 42006, p. 29-34Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Löfström, Charlotta
    et al.
    DTU Technical University of Denmark, Denmark.
    Schelin, J.
    Norling, B.
    Vigre, H.
    Hoorfar, J.
    Rådström, P.
    Culture-independent quantification of Salmonella enterica in carcass gauze swabs by flotation prior to real-time PCR2011In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no SUPPL. 1, p. S103-S109Article in journal (Refereed)
    Abstract [en]

    To facilitate quantitative risk assessment in the meat production chain, there is a need for culture-independent quantification methods. The aim of this study was to evaluate the use of flotation, a non-destructive sample preparation method based on traditional buoyant density centrifugation, for culture-independent quantification of intact Salmonella in pig carcass gauze swabs (100cm2) prior to quantitative PCR (qPCR). A novel approach was investigated, excluding the homogenization step prior to flotation, to improve the detection limit and speed up the quantification procedure. The buoyant density of two Salmonella strains in different growth conditions was determined to be 1.065-1.092g/ml. Based on these data, an optimal discontinuous flotation with three different density layers, ~1.200, 1.102 and 1.055g/ml, was designed for extracting intact Salmonella cells from pig carcass swabs. The method allowed accurate quantification from 4.4×102 to at least 2.2×107CFU Salmonella per swab sample using qPCR (without preceding DNA extraction) or selective plating on xylose lysine deoxycholate agar. Samples with 50CFU could be detected occasionally but fell outside the linear range of the standard curve. The swab samples showed a broad biological diversity; for seven samples not inoculated with Salmonella, the microbial background flora (BGF) was determined to 5.0±2.2 log CFU/ml sample withdrawn after flotation. It was determined that the proceeding PCR step was inhibited by BGF concentrations of ≥6.1×108CFU/swab sample, but not by concentrations ≤6.1×106CFU/swab sample. By using the gauze swabs directly in the flotation procedure, the homogenization step normally used for preparation of food-related samples could be excluded, which simplified the culture-independent quantification method considerably. © 2010 Elsevier B.V.

  • 17. Ronner, A.-C.
    et al.
    Engvall, E.O.
    Andersson, L.
    Kaijser, B.
    Species identification by genotyping and determination of antibiotic resistance in Campylobacter jejuni and Campylobacter coli from humans and chickens in Sweden2004In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 96, no 2, p. 173-179Article in journal (Refereed)
    Abstract [en]

    Campylobacter is today the most common cause of human bacterial enteritis in Sweden, as well as in most other industrialized countries. Common sources of infection are undercooked chicken meat, unpasteurized milk and contaminated drinking water. One aim with our present study was to identify the species Campylobacter jejuni and Campylobacter coli strains from humans and chickens using a polymerase chain reaction/restriction enzyme analysis (PCR/REA) method, as well as traditional hippurate hydrolysis test. Another aim was to investigate the antibiotic resistance pattern of the human domestic C. jejuni/C. coli isolates from infected patients and isolates from healthy Swedish chicken, as well as isolates from humans infected abroad. If discrimination between C. jejuni and C. coli was based on testing for hippurate hydrolysis, 95% of the human domestic strains and 88% of the chicken strains were identified as C. jejuni. Based on genotyping by PCR/REA, 100% of the human domestic strains and 98% of the chicken strains were attributed to C. jejuni. The E-test and disc diffusion methods were used for phenotypic antibiotic resistance studies. The two methods gave similar results. Most Swedish C. jejuni/C. coli isolates both from humans and chickens were sensitive to doxycycline and erythromycin, which are antibiotics used to treat human infection. Only 7% of the human domestic strains and 2% of the chicken strains were resistant to the quinolones tested. As a comparison, more than 94% of strains isolated from travelers to Asia and southern Europe showed antibiotic resistance to one or more drugs. © 2004 Elsevier B.V. All rights reserved.

  • 18. Suihko, M.-L.
    et al.
    Salo, S.
    Niclasen, O.
    Gudbjornsdottir, B.
    Torkelsson, G.
    Bredholt, S.
    Characterization of Listeria monocytogenes isolates from the meat, poultry and seafood industries by automated ribotyping2002In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 72, no 42006, p. 137-146Article in journal (Refereed)
    Abstract [en]

    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. van Hoek, A. H. A. M.
    et al.
    de Jonge, R.
    van Overbeek, W. M.
    Bouw, E.
    Pielaat, A.
    Smid, J. H.
    Malorny, B.
    DTU Technical University of Denmark, Denmark.
    Junker, E.
    Löfström, Charlotta
    Pedersen, K.
    Aarts, H. J. M.
    Heres, L.
    A quantitative approach towards a better understanding of the dynamics of Salmonella spp. in a pork slaughter-line2012In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 153, no 1-2, p. 45-52Article in journal (Refereed)
    Abstract [en]

    Pork contributes significantly to the public health disease burden caused by Salmonella infections. During the slaughter process pig carcasses can become contaminated with Salmonella. Contamination at the slaughter-line is initiated by pigs carrying Salmonella on their skin or in their faeces. Another contamination route could be resident flora present on the slaughter equipment. To unravel the contribution of these two potential sources of Salmonella a quantitative study was conducted. Process equipment (belly openers and carcass splitters), faeces and carcasses (skin and cutting surfaces) along the slaughter-line were sampled at 11 sampling days spanning a period of 4. months.Most samples taken directly after killing were positive for Salmonella. On 96.6% of the skin samples Salmonella was identified, whereas a lower number of animals tested positive in their rectum (62.5%). The prevalence of Salmonella clearly declined on the carcasses at the re-work station, either on the cut section or on the skin of the carcass or both (35.9%). Throughout the sampling period of the slaughter-line the total number of Salmonella per animal was almost 2log lower at the re-work station in comparison to directly after slaughter.Seven different serovars were identified during the study with S. Derby (41%) and S. Typhimurium (29%) as the most prominent types. A recurring S. Rissen contamination of one of the carcass splitters indicated the presence of an endemic 'house flora' in the slaughterhouse studied. On many instances several serotypes per individual sample were found.The enumeration of Salmonella and the genotyping data gave unique insight in the dynamics of transmission of this pathogen in a slaughter-line. The data of the presented study support the hypothesis that resident flora on slaughter equipment was a relevant source for contamination of pork. © 2011 Elsevier B.V.

  • 20. Wallin-Carlquist, N.
    et al.
    Marta, D.
    Borch, Elisabeth
    SIK – Institutet för livsmedel och bioteknik.
    Radstrom, P.
    Prolonged expression and production of Staphylococcus aureus enterotoxin A in processed pork meat2010In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 141, no SUPPL., p. S69-S74Article in journal (Refereed)
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