Phenotypic and genotypic study of antibiotic-resistant Escherichia coli isolates from a wastewater treatment plant in Zulia state, Venezuela.

Antibiotic-resistance in bacteria is a global health problem, and wastewater treatment plants can play a role in their dissemination. In this work, we used PCR and plasmid transformation to characterize antibiotic-resistance and the phylogenetic groups of Escherichia coli isolated from a treatment plant in Zulia, a state in western Venezuela. Thirty-six bacteria isolates were analyzed, of which 27 resulted resistant by disc diffusion primarily to tetracycline and sulfisoxazole but also to trimethoprim, chloramphenicol, ampicillin, and ciprofloxacin. The tetA, sul2, floR, and blaTEM resistance genes were frequently present and, in most cases, transferable. dfrA12, tetB, sul3, sul1, and aadA2 genes also were detected. The integrase gene intI1 was common in multidrugresistant isolates. These results suggest that E. coli from the treatment plant is a reservoir of antibiotic-resistance genes, which signify a potential health threat. Additionally, the phylogroup C was predominant, which is unusual and may represent an adaptation of this group to environmental conditions or perhaps the most frequent phylogroup entering from the influent.