Baseline Investigation of Non-Wild-Type Bacterial Indicators and Antibiotic Resistance Genes in Urban Wastewater from Patras, Greece

Antimicrobial resistance (AMR) is a major public health concern, and wastewater monitoring can complement clinical surveillance by capturing resistance signals at the population level. This exploratory study assessed selected antibiotic-resistant bacteria and antimicrobial resistance genes (ARGs) in untreated influent wastewater from the municipal wastewater treatment plant of Patras, Greece. Escherichia coli, Pseudomonas aeruginosa, and Enterococcus spp. were isolated using culture-based methods, tested for antimicrobial susceptibility by disk diffusion and Etest according to EUCAST epidemiological cut-off values, and screened by real-time PCR for intI1, sul1, qnrS1, blaTEM, blaVIM, vanA, and ermB. Among 16 E. coli isolates, non-wild-type (non-WT) profiles were detected on 14/16 for meropenem and 15/16 for ciprofloxacin, whereas only 1/16 was non-WT for ampicillin. All 13 P. aeruginosa isolates were wild type (WT) for meropenem but non-WT for ciprofloxacin, while all 17 Enterococcus spp. isolates were WT for vancomycin and ampicillin. Molecular screening showed that blaTEM was the most frequently detected gene in E. coli, while intI1 and sul1 were detected in subsets of P. aeruginosa isolates. No targeted ARGs were detected in Enterococcus spp. These findings provide preliminary, site-specific baseline information on selected AMR phenotypes and genetic determinants in wastewater-derived bacterial isolates from Patras.