Antibiotic resistance, pathotypes, and pathogen-host interactions in Escherichia coli from hospital wastewater in Bulawayo, Zimbabwe

This study aimed to characterise E. coli strains isolated from hospital wastewater effluent in Bulawayo, Zimbabwe, using both molecular and cytological approaches. Wastewater samples were aseptically collected from the sewerage mains of a major public referral hospital in Bulawayo province weekly for one month. A total of 94 isolates were isolated and confirmed as E. coli through biotyping and PCR targeting the uidA housekeeping gene. A total of 7 genes (eagg, eaeA, stx, flicH7, ipaH, lt, and st genes) coding for virulence in diarrheagenic E. coli were targeted. Antibiotic susceptibility of E. coli was determined against a panel of 12 antibiotics through the disk diffusion assay. The infectivity status of the observed pathotypes was investigated using HeLa cells through adherence, invasion, and intracellular assay. None of the 94 isolates tested positive for the ipaH and flicH7genes. However, 48 (53.3%) isolates were enterotoxigenic E. coli (ETEC) (lt gene positive), 2 (2.13%) isolates were enteroaggregative E. coli (EAEC) (eagg gene), and 1 (1.06%) isolate was enterohaemorrhagic E. coli (EHEC) (stx and eaeA). A high level of sensitivity was observed in E. coli against ertapenem (98.9%), and Azithromycin (75.5%). The highest resistance was against ampicillin (92.6%) and sulphamethoxazole-trimethoprim (90.4%). Seventy-nine (84%) E. coli isolates exhibited multidrug resistance. The infectivity study results indicated that environmentally isolated pathotypes were as infective as the clinically isolated pathotypes for all three parameters. No adherent cells were observed using ETEC, and no cells were observed in the intracellular survival assay using EAEC. This study revealed that hospital wastewater is a hotspot for pathogenic E. coli and that the environmentally isolated pathotypes maintained their ability to colonise and infect mammalian cells.