Virulence Characteristics and Antimicrobial Resistance Profiles of Shiga Toxin-Producing Escherichia coli Isolates from Humans in South Africa: 2006-2013

Shiga toxin-producing Escherichia coli (STEC) isolates (N = 38) that were incriminated in human disease from 2006 to 2013 in South Africa were characterized by serotype, virulence-associated genes, antimicrobial resistance and pulsed-field gel electrophoresis (PFGE). The isolates belonged to 11 O: H serotypes. STEC O26: H11 (24%) was the most frequent serotype associated with human disease, followed by O111: H8 (16%), O157: H7 (13%) and O117: H7 (13%). The majority of isolates were positive for key virulence-associated genes including stx1 (84%), eaeA (61%), ehxA (68.4%) and espP (55%), but lacked stx2 (29%), katP (42%), etpD (16%), saa (16%) and subA (3%). stx2 positive isolates carried stx2c (26%) and /or stx2d (26%) subtypes. All pathogenicity island encoded virulence marker genes were detected in all (100%) isolates except nleA (47%), nleC (84%) and nleD (76%). Multidrug resistance was observed in 89% of isolates. PFGE revealed 34 profiles with eight distinct clusters that shared 80% intra-serotype similarity, regardless of the year of isolation. In conclusion, STEC isolates that were implicated in human disease between 2006 and 2013 in South Africa were mainly non-O157 strains which possessed virulence genes and markers commonly associated with STEC strains that have been incriminated in mild to severe human disease worldwide. Improved STEC monitoring and surveillance programs are needed in South Africa to control and prevent STEC disease in humans.