Multidrug-resistant E. Coli in wastewater sources: a comparative study and identification of resistance hotspots

This work aims to study the patterns of resistance to antibiotics in wastewater samples collected from hospitals, the community, and the wastewater treatment plant using the indicator bacterium Escherichia coli. In addition, studying the phylogenetic type and screening for beta-lactamase-producing and diarrhoeagenic E. coli.

The isolates were subjected to antibiotic sensitivity tests using the Kirby-Bauer disc diffusion method using 11 antibiotics. Conventional PCR was performed for the detection of E. coli that produces beta-lactamase, as well as for the phylogenetic typing of isolates and to detect diarrheagenic strains.

From 120 wastewater samples, 92 E. coli strains were recovered and among them 66.3% were resistant. The highest resistance of isolates was observed in ampicillin/sulbactam with a moderately high rate of 37%, while the lowest resistance was reported in gentamycin at a low rate of 3.3%. Hospital wastewater isolates (HW) (75%) were more resistant than community wastewater isolates (CW) (50%). A high rate of resistance was reported in tetracycline (46.9%) among the hospital wastewater isolates, while a moderate rate of resistance was detected among community wastewater isolates to aztreonam (22.2%), making them the least effective antibiotics in these groups. More resistant isolates were found in WWTP influent (83.3%) than in effluent (44.4%). However, effluent isolates showed higher resistance to certain antibiotics, including cefepime (11.1% vs. 8.3%), piperacillin/tazobactam (11.1% vs. 4.2%), and imipenem (5.6% vs. 4.2%), than the influent. E. coli strains that showed MDR phenotype were 42.6% of resistant strains, with higher prevalence among HW (50%) and WWTPs influent (45%) than WWTPs effluent (37.5%) and CW (22.2%). Although resistance to Access antibiotics was the highest across all sources, it was comparable to the resistance observed for Watch antibiotics. At least one of the tested beta-lactamase genes was detected in 67.39% of beta-lactam-resistant E. coli strains, with bla_TEM (62.1%) and bla_OXA-48 (24.1%) being the highest prevalent among ESBLs and carbapenemase genes, respectively. About 83.69% of strains were commensal, while only 16.26% were pathogenic, in the form of enterotoxigenic E. coli; diarrheagenic E. coli was detected in 4.26% of strains.

Even though resistance was less in community wastewater than hospital wastewater, community outlets might be a source of spreading resistance. Furthermore, wastewater treatment might not be enough to eliminate resistant bacteria from the effluent; as a result, the effluent quality should be continuously monitored and evaluated.