Prevalence of EnterohemorrhagicEscherichia coliSerotypes in Australian Beef Cattle

Abstract

Beef cattle are known reservoirs of Escherichia coli O157; therefore, it is possible that they may be reservoirs for other enterohemorrhagic E. coli (EHEC) serotypes. This study investigated the prevalence of EHEC serotypes O26, O45, O91, O103, O111, O121, O145, and O157 in 300 beef cattle fecal samples. A combination of 300 (140 grain-fed and 160 grass-fed) cattle fecal samples were collected post-evisceration from Australian abattoirs. Enriched samples were tested for the putative virulence markers stx₁, stx₂, and eae using real-time PCR. Samples that tested positive for stx and eae were then tested for the target serotypes. Isolation was performed on any sample testing positive to stx and eae, and a target serotype using immunomagnetic separation for serotypes O26, O103, O111, O145, and O157 or colony hybridization for serotypes where immunomagnetic separation beads were not commercially available (O45, O91, and O121). Resulting isolates were characterized for the presence of stx₁, stx₂, eae, and ehxA using a multiplex PCR. Seventy-eight of the 300 samples (26%) were shown to contain stx and eae with 30 of these subsequently testing positive for the presence of at least one EHEC serotype. Of the 27 E. coli of EHEC serotypes isolated during the study, only 1 E. coli O91, 1 E. coli O26, and 5 E. coli O157 tested positive for the presence of any EHEC virulence markers. This study found that the overall prevalence of EHEC in Australian beef cattle is very low. Testing for the presence of virulence determinants and O-specific genes alone will overestimate the presence of pathogenic serotypes in beef. Isolation of strains of interest and confirming the presence of virulence determinants in those strains should be an essential part of any test protocol.