Virulence Properties and Serotypes of Shiga Toxin-Producing <i>Escherichia coli</i> from Healthy Australian Slaughter-Age Sheep

A group of 1,623 ovine fecal samples recovered from 65 geographically distinct mutton sheep and prime lamb properties across New South Wales, Australia, were screened for the presence of Shiga toxin-producing Escherichia coli (STEC) virulence factors (stx(1), stx(2), eaeA, and ehxA). A subset was cultured for STEC isolates containing associated virulence factors (eaeA and/or ehxA), which were isolated from 17 of 20 (85%) and 19 of 20 (95%) tested prime lamb and mutton sheep properties, respectively. STEC isolates containing stx(1), stx(2), and ehxA were most commonly isolated (19 of 40 flocks; 47.5%), and this profile was observed for 10 different serotypes. Among 90 STEC isolates studied, the most common serotypes were O91:H(-) (22 isolates [24.4%]), O5:H(-) (16 isolates [17.8%]), O128:H2 (11 isolates [12.2%]), O123:H(-) (8 isolates [8.9%]), and O85:H49 (5 isolates [5.6%]). Two isolates (2.2%) were typed as O157:H(-). A total of 78 of 90 STEC isolates (86.7%) expressed Shiga toxin in Vero cell culture and 75 of 84 ehxA-positive isolates (89.3%) expressed enterohemolysin on washed sheep blood agar. eaeA was observed in 11 of 90 (12.2%) ovine STEC isolates, including serotypes O5:H(-), O84:H(-), O85:H49, O123:H(-) O136:H40, and O157:H(-). Although only 2 of 90 isolates were typed as O157:H(-), the predominant serotypes recovered during this study have been recovered from human patients with clinical disease, albeit rarely.