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

Abstract

27Wastewater treatment plants (WWTPs) provide optimal conditions for the maintenance and 28 spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In this 29 work we describe the occurrence of antibiotic resistant faecal coliforms and their mechanisms 30 of antibiotic resistance in the effluent of two urban WWTPs in Ireland. Effluent samples were 31 collected from two WWTPs in Spring and Autumn of 2015 and 2016. The bacterial 32 susceptibility patterns to 13 antibiotics were determined. The phenotypic tests were carried 33 out to identify AmpC or extended-spectrum β-lactamase (ESBL) producers. The presence of 34 ESBL genes were detected by PCR. Plasmids carrying ESBL genes were transformed into 35Escherichia coli DH5α recipient and underwent plasmid replicon typing to identify 36 incompatibility groups. More than 90% of isolated faecal coliforms were resistant to 37 amoxicillin and ampicillin, followed by tetracycline (up to 39.82%), ciprofloxacin (up to 38 31.42%) and trimethoprim (up to 37.61%). Faecal coliforms resistant to colistin and 39 imipenem were detected in all effluent samples. Up to 53.98% of isolated faecal coliforms 40 expressed a multi-drug resistance (MRD) phenotype. AmpC production was confirmed in 41 5.22% of isolates. The ESBL genes were confirmed for 11.84% of isolates (9.2% of isolates 42 carried bla TEM , 1.4% bla , 0.2% bla CTX-M-1 and 1% bla CTX-M-15 ). Plasmids extracted from 43 52 ESBL isolates were successfully transformed into recipient E. coli. The detected plasmid 44 incompatibility groups included the IncF group, IncI1, IncHI1/2 and IncA/C. These results 45 provide evidence that treated wastewater is polluted with ARB and MDR faecal coliforms 46 and are sources of ESBL-producing, carbapenem and colistin resistant Enterobacteriaceae. 47 48 49 50 Keywords 51 Antibiotic resistance, multidrug resistance, AmpC, extended-spectrum β-lactamase (ESBL), 52 plasmids 53 54 55 56 3 57 Importance 58 Antibiotic resistant bacteria (ARB) are an emerging environmental concern with a potential 59 impact on human health. The results provide the evidence that treated wastewater is polluted 60 with antibiotic resistant bacteria containing mobile resistance mechanisms of importance to 61 clinical treatment of pathogens and multi-drug resistant (MDR) faecal coliforms. They are 62 sources of relatively high proportions of ESBL-producing Enterobacteriaceae, and include 63 carbapenem and colistin resistant Enterobacteriaceae. The significance of this study is the 64 identification of the role of WWTPs as a potential control point to reduce or stop the 65 movement of ESBL, MDR and colistin resistant bacteria into the environment from further 66 upstream sources, such as human or animal waste.

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“…‘Hard’ engineering solutions include the removal of antibiotic resistance in aqueous systems through the application of conventional and advanced water and wastewater treatment methods ( Sanganyado and Gwenzi, 2019 ). Conventional water treatment methods such as filtration have limited capacity to remove antibiotic resistance, while chlorination forms carcinogenic disinfection by-products ( Hiller et al, 2019 ; Sanganyado and Gwenzi, 2019 ; Smyth et al, 2020 ). Thus, advanced oxidation methods with high removal efficiencies are often used.…”

“…Existing literature, including reviews, is dominated by studies investigating the occurrence and behaviour of antibiotic resistance in municipal and industrial wastewaters ( Rizzo et al, 2013 ; Gwenzi et al, 2018 ; Smyth et al, 2020 ). Other studies investigated the removal of antibiotic resistance in wastewaters using various techniques ( Zhou et al, 2020 ).…”