ABSTRACT

Background and Aim: Environmental antimicrobial resistance (AMR) is an emerging One Health concern, yet district level evidence integrating surface water and groundwater remains limited in Sri Lanka. This study aimed to determine Escherichia coli contamination, characterize antimicrobial susceptibility, and compare AMR profiles between surface water and groundwater sources in Gampaha District, Sri Lanka.

Materials and Methods: A descriptive cross-sectional study was conducted from November 2023 to November 2024. A total of 104 surface water samples were collected from 52 major water bodies, while 161 groundwater samples were obtained through routine surveillance. E. coli was isolated by membrane-filtration and confirmed using biochemical tests. Antimicrobial susceptibility was evaluated by Kirby–Bauer disk diffusion against 10 antibiotics according to Clinical and Laboratory Standards Institute guidelines. Extended-spectrum beta-lactamase (ESBL) and AmpC production were assessed phenotypically. Multidrug resistance (MDR) was defined as resistance to ≥1 agent in ≥3 antimicrobial classes.

Results: All 52 surface water sites were contaminated with E. coli, and 68.3% (71/104) of samples contained ≥200 colony-forming units/100 mL. Among groundwater samples, 52.2% (84/161) were E. coli-positive. Ninety-three surface water and 84 groundwater isolates were analyzed for AMR. Nonsusceptibility to to ≥1 antibiotic occurred in 64.5% and 59.5% of surface water and groundwater isolates, respectively. MDR prevalence was comparable between sources (19.4% vs. 19.0%). Ampicillin showed the highest nonsusceptibility (54.8% vs. 45.2%). ESBL-producing isolates occurred in 5.4% and 1.2%, whereas presumptive AmpC producers occurred in 0% and 2.4% of surface water and groundwater isolates, respectively. All isolates were susceptible to ertapenem. Resistance-category distributions did not differ significantly between water sources (χ² = 2.277, df = 3, p = 0.517).

Conclusion: Widespread fecal contamination and clinically relevant AMR occur across surface water and groundwater in Gampaha District despite substantial differences in contamination intensity. Comparable MDR burdens across both sources highlight environmental dissemination of resistant E. coli and support integrated One Health surveillance. The findings provide a district level environmental AMR baseline for targeted interventions and future molecular and quantitative microbial risk assessments.

Keywords: antimicrobial resistance, environmental surveillance, Escherichia coli, extended-spectrum beta-lactamase, groundwater, multidrug resistance, One Health, surface water.