Institut für Lebensmittelwissenschaft und Biotechnologie

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Untersuchungen zur spezifischen Genexpression von enterohämorrhagischen Escherichia coli (EHEC) in der Lebensmittelmatrix
(2012) Kroj, Andrea; Schmidt, Herbert
Ground beef as a high risk food is known to be an cause of human infection with Shiga toxin-producing E. coli (STEC). The pathogens infect humans by the ingestion of undercooked ground meat and cause severe diseases like hemorrhagic colitis or the life-threatening hemolytic uremic syndrome. E. coli O157:H7 strain EDL933 as a representative of enterohemorrhagic E. coli (EHEC), a subgroup of STEC, was analysed for in vivo induced genes in ground beef with the help of the in vivo expression technology. It could be demonstrated that the promoter selection vector pKK232-8, which contains a promoterless chloramphenicol resistance gene, is not a suitable vector for a study of gene expression in this matrix. The detection of in vivo expressed genes using the alcohol-soluble and bacteriostatic antibiotic was not possible. Therefore, the promoter selection vector pAK-1 was developed. The new vector system was based on a water-soluble and bactericidal kanamycin resistance gene for selection. In the present study, the vector was established and used for analysis of the gene expression in ground meat. 20 in vivo induced genes that were expressed during growth in ground meat under elevated temperature conditions at 42°C could be detected. Eight genes were associated with energy and nucleotide metabolism, macromolecule synthesis, transport and stress response of the cell. The major part of 12 genes was attributed to a putative or unknown function. Predominantly, identified genes could not be associated with virulence or stress response of the cell. The results of this study, using the in vivo expression technology, showed that genes which are expressed under specific conditions in ground meat could be detected with the help of the chosen method. A first insight into the gene expression of strain EDL933 in ground beef could be acquired. During further investigations a comparison of the fitness of 23 E. coli strains belonging to serogroups O26, O103 and O157 was realized. The isolates originating from foods, patients with HUS and animals were compared in ground beef. The determined differences showed strain-specificity and temperature-specificty. The fitness of the strains varied dependent on the chosen temperatures at 15, 20 and 37 degrees. The analysis of the strains based on ten virulence factors showed that the observed differences could not be attributed to the presence or the number of virulence genes. A correlation between the fitness and the production of a bacteriocin could not be found.

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