Virulence and plasmidic resistance determinants of Escherichia coli isolated from municipal and hospital wastewater treatment plants

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Escherichia coli is simultaneously an indicator of water contamination and a human pathogen. This study aimed to characterize the virulence and resistance of E. coli from municipal and hospital wastewater treatment plants (WWTPs) in central Portugal. From a total of 193 isolates showing reduced susceptibility to cefotaxime and/or nalidixic acid, 20 E. coli with genetically distinct fingerprint profiles were selected and characterized. Resistance to antimicrobials was determined using the disc diffusion method. Extended spectrum β-lactamase and plasmid-mediated quinolone resistance genes, phylogroups, pathogenicity islands (PAIs) and virulence genes were screened by polymerase chain reaction (PCR). CTX-M producers were typed by multilocus sequence typing. Resistance to beta-lactams was associated with the presence of blaTEM, blaSHV, blaCTX-M-15 and blaCTX-M-32. Plasmid-mediated quinolone resistance was associated with qnrA, qnrS and aac(6′)-Ib-cr. Aminoglycoside resistance and multidrug-resistant phenotypes were also detected. PAI IV536, PAI IICFT073, PAI II536 and PAI ICFT073, and uropathogenic genes iutA, papAH and sfa/foc were detected. With regard to the clinical ST131 clone, it carried blaCTX-M-15, blaTEM-type, qnrS and aac(6′)-lb-cr; IncF and IncP plasmids, and virulence factors PAI IV536, PAI ICFT073, PAI IICFT073, iutA, sfa/foc and papAH were identified in the effluent of a hospital plant. WWTPs contribute to the dissemination of virulent and resistant bacteria in water ecosystems, constituting an environmental and public health risk.

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