Virulence markers in shiga toxin-producing Escherichia coli isolated from cattle

This study identified potential virulence markers in 93 eae-positive and 17 9 eae-negative Shiga toxin-producing Escherichia coli (STEC), isolated from a random sampling of healthy cattle in southwestern Ontario. PCR amplifica tion was used to identify genes for enterohemorrhagic E. coli (EHEC)-hemoly sin, the EAF plasmid, and bundle-forming pill (Bfp); adherence to HEp-2 cel ls and to bovine colonocytes, and the fluorescent actin staining (FAS) test were used to characterize interaction of the bacteria with epithelial cell s. The EHEC-hemolysin sequences were detected in 98% of eae-positive isolat es compared with 34% of eae-negative isolates. All isolates were negative f or EAF and bfp sequences. There was 100% correlation between localized adhe rence (LA) to HEp-2 cells and the FAS test. Forty-eight (52%) of the eae-po sitive isolates were LA/FAS-positive, whereas none of the 179 eae-negative isolates was positive in either test. Among the eae-negative isolates, 20 ( 11%) showed diffuse adherence and 5 (2.8%) showed enteroaggregative adheren ce to HEp-2 cells. Seventy-three percent of the eae-positive isolates adher ed to bovine colonocytes, whereas only 26% of 120 eae-negative isolates tha t were tested adhered. All 13 O157:H7 isolates were positive for eae and EH EC-hemolysin gene sequences, LA/FAS, and adherence to bovine colonocytes. I t is concluded that possession of genes for eae and EHEC hemolysin is corre lated with the serotype of STEC, that production of EHEC hemolysin was high ly correlated with serotypes implicated in human disease, and that none of the potential markers that were examined can be used to predict the potenti al virulence of an isolate.