Resistance Patterns of Antibiotic-Resistant Bacteria in Urban Wastewater

Background

Antimicrobial resistance (AMR) is a major public health threat, and urban wastewater is a useful community-level matrix for monitoring resistant bacteria and antimicrobial resistance genes (ARGs). This study assessed antibiotic-resistant bacterial indicators and selected ARGs in untreated urban wastewater to support wastewater-based AMR surveillance.

Methods

A descriptive surveillance study was conducted at the wastewater treatment plant of Patras, Greece, serving approximately 200,000 inhabitants. Untreated influent samples were cultured for Escherichia coli, Pseudomonas aeruginosa, and Enterococci spp. Isolates were identified phenotypically and tested by disk diffusion and Etest according to EUCAST epidemiological cut-offs. ARGs were detected using real-time qPCR for int1, sul1, qnrS1, blaTEM, blaVIM, ermB, vanA, and gyrA.

Results

Preliminary phenotypic data showed extensive non-wild-type profiles. All E. coli isolates were non-wild type for meropenem and ciprofloxacin (13/13), while ampicillin non-wild-type profiles were detected in 1/13. All P. aeruginosa isolates were non-wild type for meropenem and ciprofloxacin (11/11). Enterococci spp. were non-wild type for vancomycin in 11/11 isolates and for erythromycin in 10/11, while ampicillin non-wild-type profiles were detected in 3/11. Molecular analysis detected blaTEM in 7/13 E. coli isolates and int1 in 1/13, whereas sul1 and qnrS were not detected. In P. aeruginosa, gyrA was detected in 11/11 isolates, and int1 and sul1 in 4/11; blaVIM was absent. In none of the Enterococci spp. isolates int1, sul1, vanA, or ermB were detected.

Conclusions

Untreated urban wastewater revealed a substantial burden of phenotypic AMR and selected ARGs at the community level. These findings support routine wastewater-based AMR surveillance as an early-warning and monitoring tool, informing antimicrobial stewardship, environmental monitoring, and local preparedness policies.

Key messages

• Urban wastewater surveillance can reveal community-level antibiotic-resistant bacteria and support early public health action.

• Routine monitoring of resistance genes in wastewater can strengthen AMR surveillance and guide local prevention policies.