Rohtraud Pichner

Shiga Toxin–producing Escherichia coli Serogroups in Food and Patients, Germany

We compared 61 Shiga toxin–producing Escherichia coli (STEC) serogroups from 448 food isolates with 71 STEC serogroups from 1,447 isolates from patients in Germany. Two thirds (41/61), representing 72% of food isolates, were also found in patients. Serogroups typically isolated from patients with hemolytic uremic syndrome were rarely found in food.

Infectivity of Scrapie Prion Protein (PrPSc) Following In vitro Digestion with Bovine Gastrointestinal Microbiota

The influence of a complex microflora residing in the gastrointestinal tract of cattle on the prion protein plays a crucial role with respect to early pathogenesis and the potential infectivity of faeces resulting in contamination of the environment. It is unknown whether infectious prion proteins, considered to be very stable, are inactivated by microbial processes in the gastrointestinal tract of animals during digestion. In our previous study it was shown that the scrapie‐associated prion protein was degraded by ruminal and colonic microbiota of cattle, as indicated by a loss of anti‐prion antibody 3F4 immunoreactivity in Western blot. Subsequently, in this study hamster bioassays with the pre‐treated samples were performed. Although the PrPSc signal was reduced up to immunochemically undetectable levels within 40 h of pre‐treatment, significant residual prion infectivity was retained after degradation of infected hamster brain through the gastrointestinal microflora of cattle. The data presented here show that the loss of anti‐prion antibody 3F4 immunoreactivity is obviously not correlated with a biological inactivation of PrPSc. These results highlight the deficiency of using Western blot in transmissible spongiform encephalopathies inactivation assessment studies and, additionally, point to the possibility of environmental contamination with faeces containing PrPSc following an oral ingestion of prions.

New insights in antibiotic resistance of Lactobacillus species from fermented foods

Abstract Bacteria belonging to the genus Lactobacillus are used as starter cultures or that develop naturally as fermenting microbiota in the production of various foods. On the detrimental side, lactobacilli may act as reservoir of antibiotic resistance genes, which can spread to commensal bacteria in humans or animals, or to food-associated pathogens. In the last decade, advances in molecular biology and in genome sequencing have provided more information on antibiotic resistances in foodborne bacteria. The aim of this review was to consider and provide an up-to-date status on phenotypic and genotypic antibiotic resistance profiles in Lactobacillus species from fermented foods and also to highlight new information on the distribution of glycopeptide and chloramphenicol resistance genes in Lactobacillus genomes. In silico screening of vanZ (glycopeptide resistance) and cat (chloramphenicol resistance)-like sequences in Lactobacillus species isolated from fermented foods revealed for the first time the occurrence of vanZ and cat genes in Lactobacillus species being highly conserved genes in the chromosome of each species, presumably non-transferable. Further studies involving genome sequences of Lactobacillus isolated from fermented foods, especially those relying on spontaneous fermentation, is crucial to increase knowledge on the potential presence and spread of antibiotic resistance genes via the food route.

The controversial nature of the Weissella genus: technological and functional aspects versus whole genome analysis-based pathogenic potential for their application in food and health.

Despite the use of several Weissella (W.) strains for biotechnological and probiotic purposes, certain species of this genus were found to act as opportunistic pathogens, while strains of W. ceti were recognized to be pathogenic for farmed rainbow trout. Herein, we investigated the pathogenic potential of weissellas based on in silico analyses of the 13 whole genome sequences available to date in the NCBI database. Our screening allowed us to find several virulence determinants such as collagen adhesins, aggregation substances, mucus-binding proteins, and hemolysins in some species. Moreover, we detected several antibiotic resistance-encoding genes, whose presence could increase the potential pathogenicity of some strains, but should not be regarded as an excluding trait for beneficial weissellas, as long as these genes are not present on mobile genetic elements. Thus, selection of weissellas intended to be used as starters or for biotechnological or probiotic purposes should be investigated regarding their safety aspects on a strain to strain basis, preferably also by genome sequencing, since nucleotide sequence heterogeneity in virulence and antibiotic resistance genes makes PCR-based screening unreliable for safety assessments. In this sense, the application of W. confusa and W. cibaria strains as starter cultures or as probiotics should be approached with caution, by carefully selecting strains that lack pathogenic potential.

Fitness of Enterohemorrhagic Escherichia coli (EHEC)/Enteroaggregative E. coli O104:H4 in Comparison to That of EHEC O157: Survival Studies in Food and In Vitro

ABSTRACT In 2011, one of the worlds largest outbreaks of hemolytic-uremic syndrome (HUS) occurred, caused by a rare Escherichia coli serotype, O104:H4, that shared the virulence profiles of Shiga toxin-producing E. coli (STEC)/enterohemorrhagic E. coli (EHEC) and enteroaggregative E. coli (EAEC). The persistence and fitness factors of the highly virulent EHEC/EAEC O104:H4 strain, grown either in food or in vitro, were compared with those of E. coli O157 outbreak-associated strains. The log reduction rates of the different EHEC strains during the maturation of fermented sausages were not significantly different. Both the O157:NM and O104:H4 serotypes could be shown by qualitative enrichment to be present after 60 days of sausage storage. Moreover, the EHEC/EAEC O104:H4 strain appeared to be more viable than E. coli O157:H7 under conditions of decreased pH and in the presence of sodium nitrite. Analysis of specific EHEC strains in experiments with an EHEC inoculation cocktail showed a dominance of EHEC/EAEC O104:H4, which could be isolated from fermented sausages for 60 days. Inhibitory activities of EHEC/EAEC O104:H4 toward several E. coli strains, including serotype O157 strains, could be determined. Our study suggests that EHEC/EAEC O104:H4 is well adapted to the multiple adverse conditions occurring in fermented raw sausages. Therefore, it is strongly recommended that STEC strain cocktails composed of several serotypes, instead of E. coli O157:H7 alone, be used in food risk assessments. The enhanced persistence of EHEC/EAEC O104:H4 as a result of its robustness, as well as the production of bacteriocins, may account for its extraordinary virulence potential. IMPORTANCE In 2011, a severe outbreak caused by an EHEC/EAEC serovar O104:H4 strain led to many HUS sequelae. In this study, the persistence of the O104:H4 strain was compared with those of other outbreak-relevant STEC strains under conditions of fermented raw sausage production. Both O157:NM and O104:H4 strains could survive longer during the production of fermented sausages than E. coli O157:H7 strains. E. coli O104:H4 was also shown to be well adapted to the multiple adverse conditions encountered in fermented sausages, and the secretion of a bacteriocin may explain the competitive advantage of this strain in an EHEC strain cocktail. Consequently, this study strongly suggests that enhanced survival and persistence, and the presumptive production of a bacteriocin, may explain the increased virulence of the O104:H4 outbreak strain. Furthermore, this strain appears to be capable of surviving in a meat product, suggesting that meat should not be excluded as a source of potential E. coli O104:H4 infection.

Stability of Bovine Spongiform Encephalopathy Prions: Absence of Prion Protein Degradation by Bovine Gut Microbiota

Bovine spongiform encephalopathy (BSE) is transmitted by the oral route. However, the impacts of anaerobic fermentation processes in cattle on the stability of BSE‐associated prion protein (PrPSc) are still unresolved. In this study, experiments were designed to assess the ability of complex ruminal and colonic contents of bovines to degrade BSE‐derived PrPSc. No significant decrease in PrPSc levels in BSE brain homogenates was detected by Western blotting after up to 66 h of co‐incubation with intestinal fluids. These results indicate that BSE‐associated PrPSc survive gastrointestinal digestion processes in cattle and might be excreted via faeces.

Acidified nitrite inhibits proliferation of Listeria monocytogenes - Transcriptional analysis of a preservation method.

Sodium nitrite (NaNO2) is added as a preservative during raw meat processing such as raw sausage production to inhibit growth of pathogenic bacteria. In the present study it was shown in challenge assays that the addition of sodium nitrite indeed inhibited growth and survival of Listeria monocytogenes in short-ripened spreadable raw sausages. Furthermore, in vitro growth analyses were performed, which took into account combinations of various parameters of the raw sausage ripening process like temperature, oxygen availability, pH, NaCl concentration, and absence or presence of NaNO2. Data based on 300 growth conditions revealed that the inhibitory effect of nitrite was most prominent in combination with acidification, a combination that is also achieved during short-ripened spreadable raw sausage production. At pH6.0 and below, L. monocytogenes was unable to replicate in the presence of 200mg/l NaNO2. During the adaptation of L. monocytogenes to acidified nitrite stress (pH6.0, 200mg/l NaNO2) in comparison to acid exposure only (pH6.0, 0mg/l NaNO2), a massive transcriptional adaptation was observed using microarray analyses. In total, 202 genes were up-regulated and 204 genes were down-regulated. In accordance with growth inhibition, a down-regulation of genes encoding for proteins which are involved in central cellular processes, like cell wall/membrane/envelope biogenesis, translation and ribosomal structure and biogenesis, transcription, and replication, recombination and repair, was observed. Among the up-regulated genes the most prominent group belonged to poorly characterized genes. A considerable fraction of the up-regulated genes has been shown previously to be up-regulated intracellularly in macrophages, after exposure to acid shock or to be part of the SigB regulon. These data indicate that the adaptation to acidified nitrite partly overlaps with the adaptation to stress conditions being present during host colonization.

Prävalenz und Kontaminationsrisikofaktoren für Salmonella spp. in Hähnchen und Hähnchenfleisch in Deutschland und der Europäischen Union

Mit Einfuhrung der EU-Verordnungen 2160/2003 und 2073/2005 sowie der Huhner-Salmonellen-Verordnung in Deutschland setzte man sich zum Ziel, die Pravalenz der Salmonella enterica-Serovare Typhimurium und Enteritidis als bedeutende Erreger humaner Salmonellosen in Geflugelbestanden und -produkten deutlich zu reduzieren. Mittlerweile zeigt sich, dass dieses Ziel in vielen Bereichen der Lebensmittelkette, wie etwa der Geflugelaufzucht und -haltung, sowohl in einem Grosteil der EU-Staaten als auch in Deutschland erreicht wurde bzw. man ihm sehr nahe gekommen ist. Weniger Beachtung bei der Bekampfung finden jedoch die Prozesse des Geflugeltransports und der -schlachtung als mogliche Kontaminationsquellen von Geflugelfleisch, die die Erfolge der Salmonellen-Bekampfung in der Aufzucht und Haltung mindern. Folglich besteht vor allem in diesen Bereichen das Potenzial fur hygienische Verbesserungen. Zudem rucken in einigen Landern bzw. Bereichen S. enterica-Serovare, die bisher von untergeordneter epidemiologischer Bedeutung waren und ein ahnliches humanpathogenes Potenzial wie S. Typhimurium und S. Enteritidis aufweisen, in den Vordergrund. Dieser Ubersichtsartikel fasst ausgehend von bisher bekannten Pravalenzdaten der Jahre 1996 bis 2011 beim Geflugel aktuelle Erkenntnisse zu moglichen Salmonellen-Kontaminationsrisiken in der Lebensmittelkette Geflugel zusammen und gibt Hinweise fur mogliche Ansatzpunkte zur weiteren Verbesserung der Situation.