Virulence profiling and disease association of verocytotoxin-producing Escherichia coli O157 and non-O157 isolates in Belgium.

Whereas the association of verocytotoxin-producing Escherichia coli (VTEC) O157:H7 with the hemolytic uremic syndrome (HUS) is well established, the medical importance of many non-O157 serotypes remains unclear. Using polymerase chain reaction (PCR), we have investigated the distribution of the pathogenicity island O island 122 (OI-122) and other virulence genes in VTEC belonging to seropathotypes (SPT) A through D, and assessed their association with human disease. Two hundred sixty-five VTEC isolated from human stools comprising 52 O157 (of which 14 associated with HUS) and 213 non-O157 isolates (of which 19 associated with HUS) were studied. A complete OI-122 (COI-122) was detected in all O157, but in only 35 (16.4%) of non-O157 strains. A progressive decrease in the frequency of COI-122 was observed from SPT A through D, with a concomitant increase in the frequencies of incomplete and absent OI-122. We focused on the variable virulence profiles of the non-O157 serotypes and found that COI-122 was also more frequently present in isolates associated with HUS (p=0.001). The individual genes vtx2, eae, espP, as well as the OI-122-associated genes sen, nleB, nleE, and the efa gene cluster were significantly more often present in non-O157 VTEC associated with HUS. Non-O157 isolates carrying the combined virulence profile vtx2-nleE-efa showed the strongest association with HUS (p<0.0001). Molecular risk assessment by determination of virulence profiles of individual isolates may be useful in the identification of highly virulent non-O157 strains. We showed that the detection of a specific gene combination could assist in identifying non-O157 VTEC isolates that pose a serious public health concern.