Dominant plasmids carrying extended-spectrum β-lactamases bla genes in genetically diverse Escherichia coli from slaughterhouse and urban wastewaters.

Wastewater treatment plants (WWTP) receiving effluents from food-producing animals and humans may contribute to the spread of extended-spectrum β-lactamases (ESBL)-carrying plasmids. This study was designed to investigate extended-spectrum cephalosporin resistant Escherichia coli strains, CTX-M distributions and the genetic lineage of bla -carrying plasmids from urban and slaughterhouse wastewaters. The level of extended-spectrum cephalosporin-resistant E. coli in slaughterhouse wastewater entering the WWTP was negligible compared with that of urban wastewater. The bla gene was predominant in slaughterhouse wastewater whereas diverse bla genes were encountered in urban wastewater and WWTP outlet. Characterization of the main CTX-M-producing E. coli isolates by antibiotic resistance phenotyping, genotyping and typing of plasmids carrying bla genes revealed that bla and bla genes were harboured by the predominant bla IncI1/ST3 and bla F31:A4:B1 plasmids, which were recovered from unrelated E. coli genotypes in both slaughterhouse and urban wastewaters. This study highlighted the spread of predominant bla and bla plasmid lineages in diverse E. coli genotypes from humans and food-producing animals, their mixing in WWTP and final release into the aquatic environment. This could have a serious negative impact on public health and requires further evaluation.