Infections resistant to broad spectrum antibiotics due to the emergence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae is of global concern. This study characterizes the resistome (i.e., entire ecology of resistance determinants) of 11 ESBL-producing Escherichia coli isolates collected from eight wastewater treatment utilities across Oregon. Whole genome sequencing was performed to identify the most abundant antibiotic resistance genes including ESBL-associated genes, virulence factors, as well as their sequence types. Moreover, the phenotypes of antibiotic resistance were characterized. ESBL-associated genes (i.e., blaCMY, blaCTX, blaSHV, blaTEM) were found in all but one of the isolates with five isolates carrying two of these genes (four with blaCTX and blaTEM; one with blaCMY and blaTEM). The ampC gene and virulence factors were present in all the E. coli isolates. Across all the isolates, 31 different antibiotic resistance genes were identified. Additionally, all E. coli isolates harbored phenotypic resistance to beta-lactams (penicillins and cephalosporins), while 8 of the 11 isolates carried multidrug resistance phenotypes (resistance to three or more classes of antibiotics). Findings highlight the risks associated with the presence of ESBL-producing E. coli isolates in wastewater systems that have the potential to enter the environment and may pose direct or indirect risks to human health.

Wastewater treatment utilities are considered one of the main sources and reservoirs of antimicrobial resistance. The objective of this study was to determine the diversity and prevalence of antibiotic-resistant Escherichia coli in wastewater treatment systems across the state of Oregon. Influent, secondary effluent, final effluent, and biosolids were collected from 17 wastewater treatment utilities across Oregon during the winter and summer seasons of 2019 and 2020 (n = 246). E. coli strains were recovered from samples by culturing on mTEC, followed by confirmation with MacConkey with MUG agar plates. Antibiotic susceptibility of 1143 E. coli isolates against 8 antibiotics were determined, and resistance profiles and indices were analyzed between utilities, seasons, and flows. Antibiotic resistance phenotypes were detected in 31.6% of the collected E. coli isolates. Among those antibiotic-resistant E. coli isolates, multi-drug resistance (i.e., resistance to three or more classes of antibiotics) was harbored by 27.7% with some strains showing resistance to up to six classes of antibiotics. The most prevalent resistance was to ampicillin (n = 207) and the most common combinations of multi-drug resistance included simultaneous resistances to ampicillin, streptomycin, and tetracycline (n = 49), followed by ampicillin, streptomycin, and sulfamethoxazole/trimethoprim (n = 46). Significant correlations were observed between resistance to sulfamethoxazole/trimethoprim and resistances to ampicillin, ciprofloxacin, and tetracycline (p < 0.001). A small percentage (1.1%) of the E. coli isolates displayed extended-spectrum beta lactamase (ESBL) activity and a single isolate carried resistance to imipenem. Compared to wastewater influent, ciprofloxacin resistance was significantly more prevalent in biosolids (p <0.05) and tetracycline resistance was significantly lower in effluent (p <0.05). Seasonal impact on antibiotic-resistant E. coli in wastewater influent was observed through significantly higher multiple antibiotic resistance (MAR) index, ampicillin resistance prevalence, and ciprofloxacin resistance prevalence in summer compared to winter (p < 0.05). This state-wide study confirms the widespread distribution of antibiotic-resistant, multi-drug resistant, and extended-spectrum beta lactamase-producing E. coli in wastewater systems across different flows and seasonal variations, making them the recipients, reservoirs, and sources of antimicrobial resistance.

Infections resistant to broad spectrum antibiotics due to the emergence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae is of global concern. This study characterizes the resistome (i.e., entire ecology of resistance determinants) of 11 ESBL-producing Escherichia coli isolates collected from eight wastewater treatment utilities across Oregon. Whole genome sequencing was performed to identify the most abundant antibiotic resistance genes including ESBL-associated genes, virulence factors, as well as their sequence types. Moreover, the phenotypes of antibiotic resistance were characterized. ESBL-associated genes (i.e., blaCMY, blaCTX, blaSHV, blaTEM) were found in all but one of the isolates with five isolates carrying two of these genes (4 with blaCTX and blaTEM; 1 with blaCMY and blaTEM). The ampC gene and virulence factors were present in all the E. coli isolates. Across all the isolates, 31 different antibiotic resistance genes were identified. Additionally, all E. coli isolates harbored phenotypic resistance to beta-lactams (penicillins and cephalosporins), while eight of the 11 isolates carried multi-drug resistance phenotypes (resistance to three or more classes of antibiotics). Findings highlight the risks associated with the presence of ESBL-producing E. coli isolates in wastewater systems that have the potential to enter the environment and may pose direct or indirect risks to human health.