Prevalence and antibiotic sensitivity of enterotoxigenic Escherichia coli isolates in South African pig population.
Sikhosana, Zizile Emelda Lilly.
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Escherichia coli (E. coli) are among the leading bacterial causes of diarrhoea and edema in newborn and weaned pigs. Pathogenic strains of E. coli are classified into enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), enteroaggreagative E. coli (EAEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC) and diffusely adherent E. coli (DAEC) based on virulence factors. Infection with E. coli is achieved by adherence of fimbrial and/or non-fimbrial adhesins to the intestines and the release of toxins thereafter. The increasing rates of antimicrobial resistance are posing a threat in the treatment of porcine E. coli infections. The aim of this study was to determine the prevalence of pathogenic Escherichia coli virulence genes and antibiotic sensitivity of enterotoxigenic Escherichia coli isolates from neonatal and post-weaning pigs in Limpopo and Eastern Cape provinces of South Africa. For this purpose, 325 rectal swabs were collected from pigs from the Eastern Cape and Limpopo provinces of South Africa to investigate the prevalence of ETEC relative to other E. coli strains. Classical microbiological tests were conducted for confirmation of E. coli and PCR was used for the detection of fimbrial, non-fimbrial adhesins and toxin genes. In addition, antimicrobial susceptibility of ETEC positive isolates was determined by the Kirby-Bauer disk diffusion method. Of the 325 swabs collected, 303 isolates were identified as E. coli with 67% (205/303) harboring at least one of the tested virulence genes (LT, STa, STb, EAST-1, Stx1, Stx2, Stx2e, VT1, VT2, hlyA, F4, F5, F6, F18, F41, AIDA-1, EAE and PAA) and categorized into 48 pathotypes. A total of 36 (11.9%) isolates was classified as ETEC, having heat-labile (LT) enterotoxin as the most prevalent. Only a single isolate (2.8%) carried fimbriae (F4/F5). Instead, non-fimbrial adhesins PAA, AIDA-1 and EAE were detected. The ETEC positive isolates displayed 47.2%, 38.9% and 36.1% resistance to oxytetracycline, ampicillin and trimetroprim respectively. Most of the ETEC isolates were sensitive to florphenicol (100%), cefotaxime (97.2%) and enrofloxacin (77.8%). Multi-drug resistance was detected in 50% of the isolates. The study demonstrated that there are various E. coli pathotypes in South Africa. The detection of non-fimbrial adhesins reinforces existing knowledge that fimbriae are not the only colonization factors associated with ETEC. Based on the antimicrobial susceptibility patterns observed, florphenicol, cefotaxime and enrofloxacin could be used for the treatment of ETEC infections in South African pigs.