Modeling gene associations for virulence classification of verocytotoxin-producing E. coli (VTEC) from patients and beef.

An evaluation of 22 EHEC genes was carried out for virulence classification of VTEC. The data consisted of 116 patient isolates and 42 beef isolates. The symptoms among patients ranged from mild (diarrhea) to severe (bloody diarrhea and HUS). A cluster of genes-efa1, eae, ecf4, paa, and ureC-were more frequent in patient isolates than beef isolates. They also contributed to the classification of high virulence isolates compared with low virulence isolates. These genes may together constitute a general virulence factor, being also associated with well-known virulence serogroups: O157, O26, O103, O111, O145, O121, and O118. In a regression model of patient versus beef isolates, the combined presence of efa1 and paa proved a particularly efficient indicator of patient isolates (OR: 32.9). In contrast, a single gene, vtx22 (subtype vtx2 of vtx2) was a relatively efficient predictor of high virulence among patient isolates (OR: 41.6), but not of virulence in general. Significant interaction effects observed between genes need to be addressed and clarified in future studies.