Molecular characterization, antibiogram and distribution of zntA gene in zinc-resistant Escherichia coli population recovered from anthropogenically-influenced surface water sources in Nigeria

Background: Anthropogenic activities have been largely responsible for the elevated concentration of metals in the environment. The presence of these metals has necessitated the acquisition of resistance mechanisms by bacteria to metals and other environmental toxicants. This study aimed at investigating the occurrence and distribution of zntA gene, and antibiogram of zinc-resistant Escherichia coli (E. coli) from selected anthropogenically-influenced surface waters in Ibadan, Nigeria. Methods: Water samples were collected and analyzed for zinc concentration using atomic absorption spectrophotometer. Zinc-resistant E. coli were isolated on CHROMagar E. coli incorporated with 1 mM of zinc salt and antibiotic susceptibility testing on the isolates was carried out using the disc diffusion method. The identity of the isolates was confirmed by detecting the presence of uidA gene using specific primers, while the detection of zinc resistance gene (zntA) was done using polymerase chain reaction (PCR). Results: The zinc concentrations in the surface water samples were: AG (6.12 mg/L), ZAR (5.54 mg/L), UB (0.01 mg/L) and OG (6.61 mg/L). A total of fifty-four zinc-resistant E. coli were obtained. The percentage resistance to the antibiotics was: ampicillin (92.6%), imipenem (77.8%), amoxicillin-clavulanate (68.5%), sulfamethoxazole-trimethoprim (53.7%), doxycycline (68.5%), cefotaxime (27.8%), ciprofloxacin (7.41%), colistin sulphate (13%), chloramphenicol (1.9%) and gentamicin (0%). zntA gene was detected in fifteen (27.8%) of the isolates, while fifty-one (94.4%) of the isolates were multidrug resistant (MDR). Conclusion: This study has confirmed that surface waters in South-west Nigeria could be potential reservoirs of metal and antibiotic resistant bacteria and their genes.