The detection and molecular characterisation of Shiga Toxigenic Escheria coli (STEC) O157 strains from humans, cattle and pigs in the North-West Province, South Africa

Abstract

The prevalence and antibiotic resistant profiles of shiga-toxin producing Escherichia coli O 157 strains isolated from faeces samples of cattle, pigs and human stool samples were determined. The strains were further characterised by molecular methods for the presence of shiga-toxin virulence genes and antibiotic resistant genes. Seventy-six Escherichia coli O 157 strains were isolated and the prevalence was higher among E. coli isolated from faeces from pigs (44.2% to 50%) than those from cattle faeces (5.4% to 20.0%) or human stool samples (7.5%). On testing E. coli 0157 isolates for their resistance to 9 antimicrobial agents, multiple antibiotic resistance (MAR) was observed in all of the isolates arising from resistance to three or more antibiotics. Seventy (92.1 % ) of the E. coli O 157 isolated from humans, cattle and pigs were resistant to tetracycline, 73 (96.1 %) were resistant to sulphamethoxazole, 63 (82.9%) were resistant to erythromycin, 40 (52.6%) were resistant to streptomycin and 26 (34.2%) were resistant to ampicillin. The highest frequency of resistance was observed among the human isolates (n=3), where 3 (100%) of the isolates were resistant to tetracycline, sulphamethoxazole, erythromycin and ampicillin. Furthermore, among the pig isolates (n=60), 58 (96.7%) were resistant to tetracycline, 57 (95%) were resistant to sulphamethoxazole, 47 (78.3%) were resistant to erythromycin, 38 (63.3%) were resistant to streptomycin and 22 (36.7%) were resistant to ampicillin. The MAR phenotypes S-Smx-T-E, Smx-T-Ap and Srnx-T-E were the dorminant phenotypes among the E. coli O 157 isolated from the faeces samples of communal pigs in 30.4%, 21.7% and 17.4% of these isolates, respectively. However, phenotypes

Smx-T-E and S-Smx-T-E-Ne were identified at 16.2% and 10.8%, respectively within the isolates obtained from commercial pig feaces. The phenotype Smx-T-E was the only MAR phenotype identified among the E. coli O 157 isolated from the feacal samples of commercial cattle at Lichtenburg. Furthermore, MAR phenotypes Smx-T-EC, K-S-Smx-T-E, S-Smx-T-E and Smx-T-E-Ap were obtained at 25%, respectively for the isolates obtained from communal cattle at Mogosane while Smx-T-E-Ap was the dorminant (66.7%) phenotype among the isolates of human origin. The phenotype Smx-T formed the basis of all the MAR phenotypes obtained and this was similar to the percentage antibiotic resistance data. The distribution of the resistant determinants for tetracycline was determined by PCR analysis in resistant isolates. A tetB gene was detected in E. coli O 157 of pig origin. Based on the characterisation of 30 isolates for the presence of STEC virulence genes by PCR, 18 (60%) possessed the hlyA gene, 7 (23.7%) possessed the eae gene and 5 (16.7%) harboured both genes. The average MAR indices for pig, cattle and human E. coli 0157 isolates were 0.4722, 0.3419 and 0.4814, respectively. Among the cattle isolates, the group MAR index was highest for the communal (Mogosane) population while the values for the commercial populations at Lichtenburg and Rustenburg were 0.33 and 0.22, respectively. E. coli 0157 isolated from pigs revealed MAR index results that were 0.508 and 0.415 for the commercial and communal populations respectively and 0.1851 for the E. coli control strains.

Characterisation by cluster analysis to determine the commonness and resolve differences between the E. coli 0157 isolated from the various sources revealed a close association between pig (Tlapeng and Mareetsane ), cattle (Mogosane) and human isolates. Interestingly, E. coli 0157 isolated from pigs occurred at the highest frequency in all the clusters, which suggested their role in the dissemination of resistant determinants.