Purpose: To determine the distribution of PAIs OI-122, OI-43/48, OI-57 and high pathogenicity island (HPI) in STEC.
Methods: STEC were classified into seropathotypes A to E based on reported occurrence in outbreaks, diarrhea and severe diseases. Specific PCR assays were used to identify eae, stx and additional virulence genes located on PAIs (OI-122: pagC, sen, efa-I, efa-II, nleB ; OI-43/48: treC, ureC, iha. aidA-1, OI-57: nleG2-3, nleG5-2, nleG6-2; HPI: fyuA, irp2).
Results: The prevalence of OI-122 and OI-57 were significantly higher in seropathotypes associated with server diseases and outbreaks than other seropathotypes (P < 0.0001). HPI was missing in seropathype A and distributed evenly in seropathotypes B, C, D and E. Most virulence genes located on OI-122, OI-43/48 and OI-57 were significantly more prevalent in seropathotypes linked to severe disease and outbreak than other seropathotypes (P < 0.0001). OI-122, OI-57 and OI-43/48 and their associated virulence genes, except pagC and iha, were found highly associated with eae-positive STEC strains, while HPI mostly occurred independently of eae presence. The β-glucuronidase-negative E. coli O157:H7 strains carried complete OI-122 and OI43/48, whereas β-glucuronidase-positive E. coli O157:H7 strains only contain parts of these PAIs.
Significance: These findings suggest that OI-122, OI-57 and OI-43/48 but not HPI are highly associated with eae-positive STEC strains and could contribute to STEC virulence. Virulence genes in PAIs that are associated with severe diseases can be used as molecular markers to identify highly virulent STEC in the food industry and public health labs.