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Molecular epidemiology of antibiotic resistant Campylobacter spp. from farm-to-fork in an intensive pig production system in Kwazulu-Natal, South Africa.

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Background: Campylobacter spp. are among the leading foodborne pathogens, causing Campylobacteriosis, a zoonotic infection that results in bacterial gastroenteritis and diarrhea disease in animals and humans. The emergence and transmission of antibiotic resistance and virulence in Campylobacter spp. is increasingly reported. We investigated the molecular epidemiology of antibiotic resistant Campylobacter spp. isolated across the farm-to-fork-continuum in an intensive pig production system in the uMgungundlovu District, Kwazulu-Natal, South Africa. Methodology: Following ethical approval, samples were collected over a period of sixteen weeks from selected critical points (farm, transport, abattoir and retail) using a farm-to-fork sampling approach according to WHO-AGISAR guidelines. Overall, 520 samples were investigated for the presence of Campylobacter spp. which were putatively identified using selective media with identity and speciation confirmed by polymerase chain reaction (PCR) of specific genes. Resistance profiles were ascertained by the Kirby-Bauer disk diffusion method according to EUCAST and/or CLSI guidelines. Selected antibiotic resistance and virulence genes were identified using PCR and DNA sequencing. Clonal relatedness among the isolates was determined using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). Results: Altogether, 378/520 (72.7%) samples were positive for Campylobacter spp. with C. coli as the most predominant (73.3%), followed by C. jejuni (17.7%) with 9.0% classified as “other”. Relatively high levels of resistance were observed in C. coli and C. jejuni to erythromycin (89% and 99%), streptomycin (87% and 93%), tetracycline (82% and 96%), ampicillin (69% and 85%), and ciprofloxacin (53% and 67%) respectively. The lowest percentage resistance observed was for gentamicin (12%) for both C. coli and C. jejuni, and nalidixic acid (28% and 27%) for C. coli and C. jejuni respectively. Multi-drug resistance (MDR) was noted among 330/378 (87.3%) isolates. The antibiotic resistance genes observed were the tetO (74.6%), the blaOXA-61 (2.9%) and cmeB (11.1%) accounting for the resistance to tetracycline and ampicillin while the membrane efflux pump could confer resistance to ampicillin, tetracycline, ciprofloxacin, and erythromycin. All C. coli and C. jejuni isolates (21) with the gyrA gene exhibited mutation at the Thr-86-Ile region in the quinolone-resistancedetermining region (QRDR) and all C. coli and C. jejuni isolates (18) exhibiting erythromycin resistance showed common transitional mutations A2075G and A2074C in the 23S rRNA gene. Of the virulence genes tested, ciaB, dnaJ, pldA, cdtA, cdtB, cdtC and cadF were detected in 48.6%, 61.1 %, 17.4%, 67.4%, 19.3%, 51% and 5% of all Campylobacter isolates respectively. The ERIC-PCR banding patterns revealed that isolates along the continuum were highly diverse with isolates from the same sampling points belonging to the same major ERIC-types. Conclusion: We showed relatively high levels of resistance to antibiotics commonly used in intensive pig production in South Africa with some evidence, albeit minimal, of transmission across the farm-tofork continuum. This together with the virulence profiles present in Campylobacter spp. presents a challenge to food safety and a potential risk to human health. This is further exacerbated by the reduction in antibiotic treatment options necessitating routine surveillance and monitoring together with antibiotic stewardship, comprehensive biosecurity, and good animal husbandry in intensive pig production.


Masters Degree. University of KwaZulu-Natal, Durban.