Evaluation of major types of shiga toxin 2e-producing escherichia coli bacteria present in food, pigs, and the environment as potential pathogens for humans

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Shiga toxin 2e (Stx2e)-producing strains from food (n = 36), slaughtered pigs (n = 25), the environment (n = 21), diseased pigs (n = 19), and humans (n = 9) were investigated for production of Stx2e by enzyme-linked immunosorbent assay, for virulence markers by PCR, and for their serotypes to evaluate their role as potential human pathogens. Stx2e production was low in 64% of all 110 strains. Stx2e production was inducible by mitomycin C but differed considerably between strains. Analysis by nucleotide sequencing and transcription of stx2e genes in high- and low-Stx2e-producing strains showed that toxin production correlated with transcription rates of stx2e genes. DNA sequences specific for the int, Q, dam, and S genes of the stx2e bacteriophage P27 were found in 109 strains, indicating cryptic P27-like prophages, although 102 of these were not complete for all genes tested. Genes encoding intimin (eae), enterohemorrhagic Escherichia coli hemolysin (ehx), or other stx1 or stx2 variants were not found, whereas genes for heat-stable enterotoxins STI, STII, or EAST1 were present in 54.5% of the strains. Seven major serotypes that were associated with diseased pigs (O138:H14, O139:H1, and O141:H4) or with slaughter pigs, food, and the environment (O8:H4, O8:H9, O100:H30, and O101:H9) accounted for 60% of all Stx2e strains. The human Stx2e isolates did not belong to these major serotypes of Stx2e strains, and high production of Stx2e in human strains was not related to diarrheal disease. The results from this study and other studies do not point to Stx2e as a pathogenicity factor for diarrhea and hemolytic uremic syndrome in humans.

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