The Experts below are selected from a list of 9522 Experts worldwide ranked by ideXlab platform
Roger Stephan - One of the best experts on this subject based on the ideXlab platform.
-
fate of shiga toxin producing and generic escherichia coli during production and ripening of semihard Raw Milk Cheese
Journal of Dairy Science, 2013Co-Authors: S Peng, Roger Stephan, Jorg Hummerjohann, Wolfgang Hoffmann, Wilhelm Bockelmann, Philipp HammerAbstract:Abstract The fate of 5 different Escherichia coli strains, including 3 Shiga toxin-producing E. coli (STEC) strains, was analyzed during the production and ripening of semihard Raw Milk Cheese. The strains, which were previously isolated from Raw Milk Cheese, were spiked into Raw Milk before Cheese production at 2 different levels (approximately 10 1 and 10 3 cfu/mL, respectively). Two Cheese types were produced, which differed in cooking temperatures (40 and 46°C). The Cheeses were sampled during manufacture and the 16-wk ripening period. An increase in E. coli counts of approximately 3.5 log 10 cfu/g occurred from Raw Milk to fresh Cheese at d 1, which was attributed to a concentration effect during Cheese production and growth of the strains. During ripening over 16wk, a slow, continuous decrease was observed for all strains. However, significant differences were found between the E. coli strains at the applied spiking levels, whereas the inactivation was similar in the 2 different Cheese types. The 2 generic E. coli strains survived at higher counts than did the 3 STEC strains. Nevertheless, only 1 of the 3 STEC strains showed significantly weaker survival at both spiking levels and in both Cheese types. Six of 16 Cheeses made from Raw Milk at a low spiking level contained more than 10cfu/g of STEC at the end of the 16-wk ripening process. After enrichment, STEC were detected in almost all Cheeses at both spiking levels. Particularly because of the low infectious dose of highly pathogenic STEC, even low colony counts in Raw Milk Cheese are a matter of concern.
-
an overview of molecular stress response mechanisms in escherichia coli contributing to survival of shiga toxin producing escherichia coli during Raw Milk Cheese production
Journal of Food Protection, 2011Co-Authors: S Peng, Jorg Hummerjohann, Taurai Tasara, Roger StephanAbstract:The ability of foodborne pathogens to survive in certain foods mainly depends on stress response mechanisms. Insight into molecular properties enabling pathogenic bacteria to survive in food is valuable for improvement of the control of pathogens during food processing. Raw Milk Cheeses are a potential source for human infections with Shiga toxin-producing Escherichia coli (STEC). In this review, we focused on the stress response mechanisms important for allowing STEC to survive Raw Milk Cheese production processes. The major components and regulation pathways for general, acid, osmotic, and heat shock stress responses in E. coli and the implications of these responses for the survival of STEC in Raw Milk Cheeses are discussed.
-
characteristics of shiga toxin producing escherichia coli isolated from swiss Raw Milk Cheese within a 3 year monitoring program
Journal of Food Protection, 2010Co-Authors: Claudio Zweifel, N Giezendanner, S Corti, Gerard Krause, J Danuser, Roger StephanAbstract:Food is an important vehicle for transmission of Shiga toxin-producing Escherichia coli (STEC). To assess the potential public health impact of STEC in Swiss Raw Milk Cheese produced from cow's, goat's, and ewe's Milk, 1,422 samples from semihard or hard Cheese and 80 samples from soft Cheese were examined for STEC, and isolated strains were further characterized. By PCR, STEC was detected after enrichment in 5.7% of the 1,502 Raw Milk Cheese samples collected at the producer level. STEC-positive samples comprised 76 semihard, 8 soft, and 1 hard Cheese. By colony hybridization, 29 STEC strains were isolated from 24 semihard and 5 soft Cheeses. Thirteen of the 24 strains typeable with O antisera belonged to the serogroups O2, O22, and O91. More than half (58.6%) of the 29 strains belonged to O:H serotypes previously isolated from humans, and STEC O22:H8, O91:H10, O91:H21, and O174:H21 have also been identified as agents of hemolytic uremic syndrome. Typing of Shiga toxin genes showed that stx(1) was only found in 2 strains, whereas 27 strains carried genes encoding for the Stx(2) group, mainly stx(2) and stx(2vh-a/b). Production of Stx(2) and Stx(2vh-a/b) subtypes might be an indicator for a severe outcome in patients. Nine strains harbored hlyA (enterohemorrhagic E. coli hemolysin), whereas none tested positive for eae (intimin). Consequently, semihard and hard Raw Milk Cheese may be a potential source of STEC, and a notable proportion of the isolated non-O157 STEC strains belonged to serotypes or harbored Shiga toxin gene variants associated with human infections.
-
prevalence and characteristics of shiga toxin producing escherichia coli in swiss Raw Milk Cheeses collected at producer level
Journal of Dairy Science, 2008Co-Authors: Roger Stephan, S Corti, Gerard Krause, J Danuser, Sandra Schumacher, Lothar BeutinAbstract:The aim of this study was to describe the prevalence, serotypes, and virulence genes of Shiga toxin-producing Escherichia coli (STEC) isolated from Raw Milk Cheese samples collected at the producer level with the purpose of determining whether Raw Milk Cheeses in Switzerland represent a potential source of STEC pathogenic for humans. Raw Milk Cheese samples (soft Cheese, n = 52; semihard and hard Cheese, n = 744; all produced from Swiss cows', goats', and sheep's Milk) collected at the producer level throughout Switzerland within the national sampling plan during the period of March 2006 to December 2007 were analyzed. Of the 432 Cheese samples obtained in the year 2006 and the 364 samples obtained in the year 2007, 16 (3.7%) and 23 (6.3%), respectively, were found to be stx positive. By colony dot-blot hybridization, non-O157 STEC strains were isolated from 16 samples. Of the 16 strains, 11 were typed into 7 E. coli O groups (O2, O15, O22, O91, O109, O113, O174), whereas 5 strains were nontypeable (ONT). Among the 16 STEC strains analyzed, stx(1) and stx(2) variants were detected in 1 and 15 strains, respectively. Out of the 15 strains with genes encoding for the Stx2 group, 4 strains were positive for stx(2), 6 strains for stx(2d2), 2 strains for stx(2-O118), 1 strain for stx(2-06), 1 strain for stx(2g), 1 strain for stx(2) and stx(2d2), and 1 strain for stx(2) and stx(2g). Furthermore, 3 STEC strains harbored E-hlyA as a further putative virulence factor. None of the strains tested positive for eae (intimin). Results obtained in this work reinforce the suggestion that semihard Raw Milk Cheese may be a potential vehicle for transmission of pathogenic STEC to humans
-
prevalence of mycobacterium avium subspecies paratuberculosis in swiss Raw Milk Cheeses collected at the retail level
Journal of Dairy Science, 2007Co-Authors: Roger Stephan, Taurai Tasara, Sandra Schumacher, Irene R GrantAbstract:A total of 143 Raw Milk Cheese samples (soft Cheese, n = 9; semihard Cheese, n = 133; hard Cheese, n = 1), collected at the retail level throughout Switzerland, were tested for Mycobacterium avium ssp. paratuberculosis (MAP) by immunomagnetic capture plus culture on 7H10-PANTA medium and in supplemented BAC-TEC 12B medium, as well as by an F57-based real-time PCR system. Furthermore, pH and water activity values were determined for each sample. Although no viable MAP cells could be cultured, 4.2% of the Raw Milk Cheese samples tested positive with the F57-based real-time PCR system, providing evidence for the presence of MAP in the Raw material. As long as the link between MAP and Crohn's disease in humans remains unclear, measures designed to minimize public exposure should also include a focus on Milk products.
Jorg Hummerjohann - One of the best experts on this subject based on the ideXlab platform.
-
short communication heat resistant escherichia coli as potential persistent reservoir of extended spectrum β lactamases and shiga toxin encoding phages in dairy
Journal of Dairy Science, 2016Co-Authors: Roger Marti, Maite Muniesa, Michael Schmid, Christian H Ahrens, J Naskova, Jorg HummerjohannAbstract:Here we report the isolation of heat-resistant Escherichia coli from Raw Milk Cheeses. Detection of the heat-resistance markers clpK and orfI by PCR was followed by phenotypical confirmation of increased heat-resistance. These strains were Shiga toxin-negative and, although several were found to be multidrug resistant, no plasmids encoding extended-spectrum β-lactamases (ESBL) were found in any of the isolates. The aim of this study was to assess the potential of these strains to acquire ESBL plasmids and a modified Shiga toxin-encoding phage. Only 4 ESBL-encoding, heat-sensitive E. coli strains were isolated from 1,251 dairy samples (2/455 Raw Milk and 2/796 Raw Milk Cheese samples). One incompatibility group FII plasmid (CTX-M-14, 79.0 kb) and 3 incompatibility group I1 plasmids (CTX-M-15, 95.2, 96.1, and 97.8 kb) were fully sequenced and de novo assembled. All 4 plasmids are readily transferred to heat-resistant E. coli isolates in plate matings (9.7×10-5 to 3.7×10-1 exconjugants per recipient) and, to a lesser extent, in Milk (up to 7.4×10-5 exconjugants per recipient). Importantly, the plasmids are stably maintained during passaging in liquid media without antimicrobial pressure. The heat-resistant isolate FAM21805 was also shown to be capable of acting as donor of all 4 ESBL plasmids. In addition, 3 of 11 tested ESBL exconjugants of heat-resistant strains were lysogenized by the modified Shiga toxin-encoding phage 933W ∆stx::gfp::cat. The higher fraction of heat-resistant E. coli (93 of 256 isolates) compared with the estimated 2% previously predicted based on genomic prevalence of heat resistance genes seems to indicate a selection advantage in the Raw Milk Cheese production environment. The combination of 2 factors may lead to said advantage: increased survival during thermization of Raw Milk (heating to subpasteurization temperatures) and increased survival rates during Cheese ripening. Should these strains acquire ESBL-encoding plasmids, Shiga toxin-encoding phages, or both, these genetic elements would profit from the selection advantage of their host and become more abundant in this particular environment, which in turn could lead to an increased threat to consumers of Raw Milk products.
-
enterotoxin producing staphylococcus aureus genotype b as a major contaminant in swiss Raw Milk Cheese
Journal of Dairy Science, 2014Co-Authors: Jorg Hummerjohann, J Naskova, A Baumgartner, H U GraberAbstract:Abstract The objective of this study was to characterize Staphylococcus aureus isolates from Swiss Raw Milk Cheeses that had been found to be contaminated with coagulase-positive staphylococci and to estimate the frequency of the various genotypes, in particular the mastitis-associated Staph. aureus genotype B (GTB). The isolates were also tested for staphylococcal enterotoxin (SE) genes and other virulence factors. From 623 coagulase-positive staphylococci isolated from 78 contaminated Raw Milk Cheeses, 609 were found to be Staphylococcus aureus . Genotyping of all Staph. aureus isolates was performed by PCR amplification of the 16S–23S rRNA intergenic spacer region, as this method was used previously to differentiate between mastitis subtypes associated with their clinical outcome. In total, 20 different genotypes were obtained and the 5 most frequently occurring genotypes were distributed in 6.4% or more of the samples. The enterotoxin-producing Staph. aureus GTB, known for its high contagiousness and increased pathogenicity in Swiss mastitis herds, was found to be the most abundant subtype at the sample level (71.8%) as well as among the isolates (62.0%). A subset of 107 isolates of the different genotypes were analyzed for the presence of SE genes and revealed 9 different SE gene patterns, with sed being most frequently detected and 26% being PCR-negative for SE genes. Almost all isolates of the major contaminant GTB contained the SE gene pattern sed , sej , ser , with half of them additionally carrying sea . Production of SE in vitro was consistent with the SE genes detected in most of the cases; however, some isolated GTB did not produce SEA. Staphylococcus aureus Protein A ( spa ) typing revealed 30 different subtypes and most GTB isolates belonged to the bovine spa type t2953; GTB/t2953 was linked among other subtypes to SE production in Cheese and staphylococcal intoxication cases. Furthermore, 1 of the 623 isolates was a methicillin-resistant Staph. aureus , which was an seh -carrying Staph. aureus spa type tbl 0635 (non-GTB). We conclude that control and reduction of enterotoxigenic Staph. aureus GTB in dairy herds in Switzerland will not only prevent economic losses at the farm level but also improve the safety of Raw Milk Cheeses; distribution of methicillin-resistant Staph. aureus via Raw Milk Cheese is of less concern.
-
fate of shiga toxin producing and generic escherichia coli during production and ripening of semihard Raw Milk Cheese
Journal of Dairy Science, 2013Co-Authors: S Peng, Roger Stephan, Jorg Hummerjohann, Wolfgang Hoffmann, Wilhelm Bockelmann, Philipp HammerAbstract:Abstract The fate of 5 different Escherichia coli strains, including 3 Shiga toxin-producing E. coli (STEC) strains, was analyzed during the production and ripening of semihard Raw Milk Cheese. The strains, which were previously isolated from Raw Milk Cheese, were spiked into Raw Milk before Cheese production at 2 different levels (approximately 10 1 and 10 3 cfu/mL, respectively). Two Cheese types were produced, which differed in cooking temperatures (40 and 46°C). The Cheeses were sampled during manufacture and the 16-wk ripening period. An increase in E. coli counts of approximately 3.5 log 10 cfu/g occurred from Raw Milk to fresh Cheese at d 1, which was attributed to a concentration effect during Cheese production and growth of the strains. During ripening over 16wk, a slow, continuous decrease was observed for all strains. However, significant differences were found between the E. coli strains at the applied spiking levels, whereas the inactivation was similar in the 2 different Cheese types. The 2 generic E. coli strains survived at higher counts than did the 3 STEC strains. Nevertheless, only 1 of the 3 STEC strains showed significantly weaker survival at both spiking levels and in both Cheese types. Six of 16 Cheeses made from Raw Milk at a low spiking level contained more than 10cfu/g of STEC at the end of the 16-wk ripening process. After enrichment, STEC were detected in almost all Cheeses at both spiking levels. Particularly because of the low infectious dose of highly pathogenic STEC, even low colony counts in Raw Milk Cheese are a matter of concern.
-
an overview of molecular stress response mechanisms in escherichia coli contributing to survival of shiga toxin producing escherichia coli during Raw Milk Cheese production
Journal of Food Protection, 2011Co-Authors: S Peng, Jorg Hummerjohann, Taurai Tasara, Roger StephanAbstract:The ability of foodborne pathogens to survive in certain foods mainly depends on stress response mechanisms. Insight into molecular properties enabling pathogenic bacteria to survive in food is valuable for improvement of the control of pathogens during food processing. Raw Milk Cheeses are a potential source for human infections with Shiga toxin-producing Escherichia coli (STEC). In this review, we focused on the stress response mechanisms important for allowing STEC to survive Raw Milk Cheese production processes. The major components and regulation pathways for general, acid, osmotic, and heat shock stress responses in E. coli and the implications of these responses for the survival of STEC in Raw Milk Cheeses are discussed.
Paula Teixeira - One of the best experts on this subject based on the ideXlab platform.
-
non thermal approach to listeria monocytogenes inactivation in Milk the combined effect of high pressure pediocin pa 1 and bacteriophage p100
Food Microbiology, 2020Co-Authors: Norton Komora, Claudia Maciel, Carlos A Pinto, Vânia Ferreira, Teresa R S Brandao, Jorge A Saraiva, Sonia Marilia Castro, Paula TeixeiraAbstract:Abstract Non-thermal food processing and replacement of chemical additives by natural antimicrobials are promising trends in the food industry. The objective of the present work was to evaluate the effect of a process which combines mild high hydrostatic pressure – HHP (200 and 300 MPa, 5 min, 10 °C), phage Listex™ P100 and the bacteriocin pediocin PA-1 as a new non-thermal process for destruction of Listeria monocytogenes (104 CFU mL−1 or 107 CFU mL−1) in Milk. For inoculum levels of 104 CFU mL−1, HHP combined with phage P100 eliminated L. monocytogenes immediately after pressurization. When L. monocytogenes was inoculated at levels of 107 CFU mL−1, a synergistic effect between phage P100, pediocin PA-1 and HHP (300 MPa) on the inactivation of L. monocytogenes was observed during storage of Milk at 4 °C. For non-pressure treated samples inoculated with phage or pediocin or both, L. monocytogenes counts decreased immediately after biocontrol application, but regrowth was observed in a few samples during storage. Phage particles were stable during refrigerated storage for seven days while pediocin PA-1 remained stable only during three days. Further studies will have to be performed to validate the findings of this work in specific applications (e.g. production of Raw Milk Cheese).
Lourdes Cabezas - One of the best experts on this subject based on the ideXlab platform.
-
biogenic amine content and proteolysis in manchego Cheese manufactured with lactobacillus paracasei subsp paracasei as adjunct and other autochthonous strains as starters
International Dairy Journal, 2015Co-Authors: Justa M. Poveda, Rosa Chicón, Lourdes CabezasAbstract:Abstract Two different autochthonous strain starter cultures, in which the acidifying starter was composed of strains of Lactococcus lactis, were used for the manufacture of pasteurised Milk Manchego Cheese. Proteolysis parameters, biogenic amines and sensory characteristics were evaluated and compared with those of commercial starter Manchego Cheese and Raw Milk Manchego Cheese manufactured without starter. Autochthonous starter Cheeses, and especially those including Lactobacillus paracasei subsp. paracasei as adjunct, presented higher levels of proteolysis than in commercial starter Cheese. The concentrations of total biogenic amines in autochthonous starter Cheeses were much lower than in Raw Milk Cheese and even lower than in commercial starter Cheese. Cheese manufactured with the adjunct strain gave the best results for both flavour intensity and flavour quality, and was the most preferred by panellists. The results suggest that the culture containing Lb. paracasei subsp. paracasei as adjunct could be used for the manufacture of industrial Manchego Cheese.
-
Volatile composition and improvement of the aroma of industrial Manchego Cheese by using Lactobacillus paracasei subsp. paracasei as adjunct and other autochthonous strains as starters
European Food Research and Technology, 2014Co-Authors: Justa M. Poveda, Pedro Nieto-arribas, Susana Seseña, Llanos Palop, Rosa Chicón, Lucía Castro, Lourdes CabezasAbstract:The use of several autochthonous strains of lactic acid bacteria, including Lactobacillus paracasei subsp . paracasei as adjunct of the starter in the manufacture of Manchego Cheese, was evaluated in an attempt to improve the aroma of the industrial Manchego Cheese. Volatile composition and odour characteristics were evaluated and compared to those in Manchego Cheese manufactured with a commercial starter (CS) culture and with Raw Milk Cheese manufactured without starter. Manchego Cheeses manufactured with two autochthonous strains of Lactococcus lactis subsp . lactis displayed a similar volatile profile and odour characteristics to the Cheese made with the CS. The use of the strain Lactobacillus paracasei subsp . paracasei CECT 7882 as adjunct of the Lactococcus strains produced Cheeses with higher amounts of some free fatty acids and alcohols, acetoin, lactones, phenylacetaldehyde, 2-phenylethanol and linalool, and higher scores of the odour intensity, odour quality, and ewe’s Milk odour than the CS Cheeses. It resulted in an intensification and improvement of industrial Manchego Cheese aroma.
Mariepierre Donguy - One of the best experts on this subject based on the ideXlab platform.
-
disentangling a complex nationwide salmonella dublin outbreak associated with Raw Milk Cheese consumption france 2015 to 2016
Eurosurveillance, 2019Co-Authors: Aymeric Ung, Amrish Baidjoe, Dieter Van Cauteren, Nizar Fawal, Laetitia Fabre, Caroline Guerrisi, Kostas Danis, Anne Morand, Mariepierre DonguyAbstract:On 18 January 2016, the French National Reference Centre for Salmonella reported to Sante publique France an excess of Salmonella enterica serotype Dublin (S. Dublin) infections. We investigated to identify the source of infection and implement control measures. Whole genome sequencing (WGS) and multilocus variable-number tandem repeat analysis (MLVA) were performed to identify microbiological clusters and links among cases, animal and food sources. Clusters were defined as isolates with less than 15 single nucleotide polymorphisms determined by WGS and/or with identical MLVA pattern. We compared different clusters of cases with other cases (case-case study) and controls recruited from a web-based cohort (case-control study) in terms of food consumption. We interviewed 63/83 (76%) cases; 2,914 controls completed a questionnaire. Both studies' findings indicated that successive S. Dublin outbreaks from different sources had occurred between November 2015 and March 2016. In the case-control study, cases of distinct WGS clusters were more likely to have consumed Morbier (adjusted odds ratio (aOR): 14; 95% confidence interval (CI): 4.8-42) or Vacherin Mont d'Or (aOR: 27; 95% CI: 6.8-105), two bovine Raw-Milk Cheeses. Based on these results, the Ministry of Agriculture launched a reinforced control plan for processing plants of Raw-Milk Cheeses in the production region, to prevent future outbreaks.
