Antibiotic resistant and extended-spectrum β-lactamase producing faecal coliforms in wastewater treatment plant effluent

Abstract

26Wastewater treatment plants (WWTPs) provide optimal conditions for the maintenance and 27 spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In this 28 work we describe the occurrence of antibiotic resistant faecal coliforms and their mechanisms 29 of antibiotic resistance in the effluent of two urban WWTPs in Ireland. Effluent samples were 30 collected from two WWTPs in Spring and Autumn of 2015 and 2016. The bacterial 31 susceptibility patterns to 13 antibiotics were determined. The phenotypic tests were carried out 32 to identify AmpC or extended-spectrum β-lactamase (ESBL) producers. The presence of ESBL 33 genes were detected by PCR. Plasmids carrying ESBL genes were transformed into 34Escherichia coli DH5α recipient and underwent plasmid replicon typing to identify 35 incompatibility groups. More than 90% of isolated faecal coliforms were resistant to 36 amoxicillin and ampicillin, followed by tetracycline (up to 39.82%), ciprofloxacin (up to 37 31.42%) and trimethoprim (up to 37.61%). Faecal coliforms resistant to colistin and imipenem 38 were detected in all effluent samples. Up to 53.98% of isolated faecal coliforms expressed a 39 multi-drug resistance (MRD) phenotype. AmpC production was confirmed in 5.22% of 40 isolates. The ESBL genes were confirmed for 11.84% of isolates (9.2% of isolates carried 41 blaTEM, 1.4% blaSHV-12, 0.2% blaCTX-M-1 and 1% blaCTX-M-15). Plasmids extracted from 52 ESBL 42 isolates were successfully transformed into recipient E. coli. The detected plasmid 43 incompatibility groups included the IncF group, IncI1, IncHI1/2 and IncA/C. These results 44 provide evidence that treated wastewater is polluted with ARB and MDR faecal coliforms and 45 are sources of ESBL-producing, carbapenem and colistin resistant Enterobacteriaceae. 46 47 48 49 Keywords 50 Antibiotic resistance, multidrug resistance, AmpC, extended-spectrum β-lactamase (ESBL), 51 plasmids 52 53 54 55 56 3