Prevalence of Type II Topoisomerase Mutations Among Quinolone Resistant Escherichia coli from Broiler Chickens in Dar es Salaam, Tanzania

Background: Quinolone-resistant Escherichia coli may easily be transmitted from poultry to humans and animals. Quinolone misuse in veterinary medicine, therefore, poses a significant public health risk. This study aimed to assess the prevalence of type II topoisomerase mutations commonly associated with resistance to quinolones in E. coli; in Dar es Salaam, Tanzania. Methods: One hundred sixty E. coli samples isolated from broiler cloacal swabs in Dar es Salaam between March and August 2022 were evaluated and analyzed for quinolone resistance by disc diffusion and genetic methods. The study used two Polymerase Chain Reaction (PCR) techniques, one a Mismatch Amplification Mutation Assay (MAMA-PCR) and the other employing enzyme digestion of amplified products (PCR-RFLP). Both approaches targeted regions in type II topoisomerases (gyrA and parC) to determine quinolone resistance (QRDR). Results: Results showed considerable levels of quinolone resistance among E. coli isolated from broiler chickens, where 42.5% of the strains demonstrated non-susceptibility to both ciprofloxacin and norfloxacin. Moreover, a significant minority of isolates (5%) were non-susceptible only to ciprofloxacin. All isolates non-susceptible to both drugs harboured a substitution mutation (S83L) at the gyrA Ser-83 target site (a resistance marker) as revealed by PCR-RFLP.  The genotypic-to-phenotypic agreement ratio for norfloxacin was 100%, in contrast to that of ciprofloxacin, which was 89.47%. However, as revealed by MAMA-PCR results, none of the isolates under study harboured parC80 (S80I) substitution mutation (a resistance marker) on the topoisomerase IV gene.  Conclusion: Type II topoisomerase mutations other than the ones assayed in this study (gyrA Ser-83 or parC80) or other mechanisms of resistance might be contributing to the resistance against quinolones in E. coli strains circulating in broiler chickens in Dar es Salaam. The level of quinolone resistance revealed by this study calls for immediate intervention to mitigate its spread.