Virulence properties and serotypes of Shiga toxin-producing Escherichia coli 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 mere 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 must 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-, O81: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.