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.
