DETECTION OF ANTIBIOTIC-RESISTANT BACTERIA IN DRINKING WATER SOURCES WITHIN THE COLOMBO DISTRICT OF SRI LANKA

Abstract

The rise of antibiotic-resistant bacteria in water distribution systems poses a significant risk to public health, particularly in regions such as Sri Lanka, where much of the infrastructure was built decades ago and may not meet present-day standards for bacterial control. This study aimed to detect the presence of antibiotic-resistant bacteria in drinking water sources within the Colombo District of Sri Lanka, focusing on two household sampling sites to which water is supplied by the National Water Supply and Drainage Board (NWSDB). Five biological replicates were analysed using various culturing methods: direct spread plating, direct quadrant streaking, and nutrient broth enrichment spread plating. This was followed by colony morphology observation, Gram staining, biochemical tests: catalase test, oxidase test, methyl-red, and Antibiotic susceptibility testing (ABST) via Kirby-Bauer disc diffusion method. The antibiotics tested were Gentamycin (10µg), Vancomycin (30µg), Ciprofloxacin (5µg), and Ampicillin (10µg). The results were analysed using Cowan and Steel’s biochemical guidelines, WHO-listed waterborne pathogens, and CLSI guidelines. No fully resistant bacterial species were observed across all samples. However, potential intermediate resistance to Ciprofloxacin (5µg) by provisional Campylobacter spp. or Pseudomonas spp. was observed across an isolate from each sampling site, validating the importance of performing routine ABST to monitor bacterial resistance trends. Statistical analysis (ANOVA) confirmed no significant variation in antibiotic response across the samples. Future work should utilise molecular methods such as PCR for bacterial species confirmation and sample collection from multiple districts to assess bacterial resistance trends.