In the ten years since its discovery, the Escherichia coli clone sequence type 131 (ST131) has become a major international health threat, with the multidrug-resistant and extended-spectrum β-lactamase (ESBL)-producing clade C emerging as the globally dominant form. ST131 has previously been isolated from wastewater; however, most of these studies selectively screened for ESBL-producing organisms, thereby missing the majority of remaining ST131 clades. In this study, we used a high-throughput PCR-based screening strategy to comprehensively examine wastewater for the presence of ST131 over a 1-year period. Additional multiplex PCRs were used to differentiate clades and obtain an unbiased account of the total ST131 population structure within the collection. Furthermore, antimicrobial susceptibility profiles of all ST131-positive samples were tested against a range of commonly used antibiotics. From a total of over 3,762 E. coli wastewater samples, 1.86% (n = 70) tested positive for ST131, with the majority being clade A isolates. In total, 63% (n = 44) were clade A, 29% (n = 20) were clade B, 1% (n = 1) were clade C0, 6% (n = 4) were clade C1, and 1% (n = 1) were clade C2. In addition, a very high rate of resistance to commonly used antibiotics among wastewater isolates is reported, with 72.7% (n = 32) of clade A resistant to ciprofloxacin and high rates of resistance to gentamicin, sulfamethoxazole-trimethoprim, and tetracycline in clades that are typically sensitive to antibiotics. IMPORTANCE ST131 is a global pathogen. This clone causes urinary tract infections and is frequently isolated from human sources. However, little is known about ST131 from environmental sources. With the widely reported increase in antibiotic concentrations found in wastewater, there is additional selection pressure for the emergence of antibiotic-resistant ST131 in this niche. The unbiased screening approach reported herein revealed that previously antibiotic-sensitive lineages of ST131 are now resistant to commonly used antibiotics present in wastewater systems and may be capable of surviving UV sterilization. This is the most comprehensive account of ST131 in the wastewater niche to date and an important step in better understanding the ecology of this global pathogen.

Wastewater treatment plants (WWTPs) have been identified as hotspots for antimicrobial resistance genes (ARGs) and thus represent a critical point where patterns in ARG abundances can be monitored prior to their release into the environment. The aim of the current study was to measure the impact of the release of the final treated effluent (FE) on the abundance of ARGs in the receiving water of a recently upgraded WWTP in the Canadian prairies. Sample nutrient content (phosphorous and nitrogen species) was measured as a proxy for WWTP functional performance, and quantitative PCR (qPCR) was used to measure the abundance of eight ARGs, the intI1 gene associated with class I integrons, and the 16S rRNA gene. The genes ermB, sul1, intI1, blaCTX-M, qnrS, and tetO all had higher abundances downstream of the WWTP, consistent with the genes with highest abundance in the FE. These findings are consistent with the increasing evidence suggesting that human activity affects the abundances of ARGs in the environment. Although the degree of risk associated with releasing ARGs into the environment is still unclear, understanding the environmental dimension of this threat will help develop informed management policies to reduce the spread of antibiotic resistance and protect public health.