National Survey of Shiga Toxin-Producing Escherichia coli Serotypes O26, O45, O103, O111, O121, O145, and O157 in Australian Beef Cattle Feces

Escherichia coli O157 and six non-O157 Shiga toxin-producing E. coli (STEC) serotypes (O26, O45, O103, O111, O121, and O145, colloquially referred to as the "big 6") have been classified as adulterants of raw nonintact beef products in the United States. While beef cattle are a known reservoir for the prototype STEC serotype, E. coli O157, less is known about the dissemination of non-O157 STEC serotypes in Australian cattle. In the present study, 1,500 fecal samples were collected at slaughter from adult (n = 628) and young (n = 286) beef cattle, adult (n = 128) and young (n = 143) dairy cattle, and veal calves (n = 315) across 31 Australian export-registered processing establishments. Fecal samples were enriched and tested for E. coli O157 and the big 6 STEC serotypes using BAX System PCR and immunomagnetic separation methods. Pathogenic STEC (pSTEC; isolates that possess stx, eae, and an O antigen marker for O157 or a big 6 serotype) were isolated from 115 samples (7.7%), of which 100 (6.7%) contained E. coli O157 and 19 (1.3%) contained a big 6 serotype. Four of the 115 samples contained multiple pSTEC serotypes. Among samples confirmed for big 6 pSTEC, 15 (1%) contained E. coli O26 and 4 (0.3%) contained E. coli O111. pSTEC of serotypes O45, O103, O121, and O145 were not isolated from any sample, even though genes indicative of E. coli belonging to these serotypes were detected by PCR. Analysis of animal classes revealed a higher pSTEC prevalence in younger animals, including veal (12.7%), young beef (9.8%), and young dairy (7.0%), than in adult animals, including adult beef (5.1%) and adult dairy (3.9%). This study is the largest of its kind undertaken in Australia. In contrast to E. coli O157 and consistent with previous findings, this study reports a relatively low prevalence of big 6 pSTEC serotypes in Australian cattle populations.