Occurrence and characterisation of the seven major Shiga toxin-producing Escherichia coli serotypes from healthy beef cattle in South Africa

Shiga toxin-producing E. coli (STEC) is a food pathogen causing infections characterised by mild watery to severe bloody diarrhea and complications such as the hemolytic uremic syndrome (HUS). Humans acquire STEC through consumption of contaminated foods of animal origin, vegetables and water. Cattle are the main reservoir of STEC. The severity of STEC infections in humans depends on a number of virulence factors encoded in the bacterium’s genome. The seven major STEC serogroups most frequently incriminated in severe human disease outbreaks and HUS worldwide include O157, O45, O103, O111, O121, O145 and, O26, commonly referred to as the "top/big seven". Although STEC has been incriminated in human disease in South Africa, data on the role of played by cattle in human disease and virulence characteristics of cattle STEC are lacking. Therefore, the objectives of this study were to (i) investigate the presence of the seven major STEC serotypes in healthy beef cattle (cow-calf operations) and (ii) characterise isolates by serotype, virulence genes and markers, and antimicrobial resistance profiles. Polymerase chain reaction (PCR) was carried out to identify STEC serotypes (O and H antigens) and characterize the isolates by virulence factors and markers. The disk diffusion technique (Kirby Bauer test) was used to determine the antimicrobial resistance profiles of STEC isolates against a panel of 15 antimicrobials. Five hundred and seventy-eight STEC isolates (N=578), which had been previously recovered from 559 cattle from five beef farms were screened for STEC O26, O45, O103, O111, O121, O145 and O157. Confirmed STEC belonging to serogroups O26, O45, O103, O111, O121, O145 and O157 to isolates were characterised for major virulence genes including stx1, stx2, eaeA and ehxA. Furthermore, 140 isolates were characterised for xiii Shiga toxins (stx) subtypes, plasmid and pathogenicity island-encoded genes, and antimicrobials resistance profiles.Dissertation (MSc)--University of Pretoria, 2017.Paraclinical SciencesMScUnrestricte