Purpose: To determine the diversity of O-serotypes and virulence markers of STEC isolates from feedlot cattle, wild birds, wild rodents, and feral pigs in a major vegetable production region of the desert southwest. Differentiation of clinically relevant STECs from those not considered a significant health risk is critical to sound testing policy.
Methods: Purified STEC strains were O-serotyped and characterized for virulence genes (stx1, stx2, eaeA, hlyA, fliC and rfbE) using conventional PCR. A subset of 36 strains was tested with STEC G2 combo (Roka Bioscience) and for putative virulence markers (ehxA, aggR, saaD and subAB).
Results: Overall, 130 E. coli O157 and 299 non-O157 STEC were detected from 750 domestic cattle and 1212 wildlife in the desert southwest during 2011-2013. PCR revealed that 94 (22%) isolates carried stx1 genes, 226 (53%) possessed stx2 genes, and 109 (25%) possessed both targets. Both hlyA and intimin eaeA were detected in 190 (44%) isolates and alone in 67 (16%) and 12 (3%) of the isolates, respectively. Multivariate logistic regression analysis of these isolates showed significant associations (P < 0.005) between the presence of both hlyA and eaeA with the presence of stx1 or stx2. Among 199 non-O157 STEC isolates, 64% belonged to six serotypes: O136 (19.2%), O156 (15.2%), O171 (8.1%), O109 (7.6%), O2 (7.1%) O160 (6.6%). Approximately 50% of the isolates analyzed with Roka were classified as STEC. One strain (feral pig) was found to carry a putative virulence gene (saaD).
Significance: The majority of STEC isolates obtained in this study were not among the “Top 6” non-O157 serotypes (O26, O111, O103, O121, O45 and O145). Rapid discrimination of clinical relevance would improve risk management decisions and, potentially, avoid unnecessary destruction of crops.