Abstract:
Background: The presence of antibiotic-resistance genes (ARGs) has been reported in river
water sources. Water treatment plants (WTPs) primarily focus on removing coliforms before
distributing chlorinated water for human consumption. However, data regarding the presence of
ARGs in chlorinated water in Sri Lanka are scarce.
Objective: To investigate the presence of ARGs in chlorinated drinking water treated by WTPs
located along the Mahaweli river
Methods: Chlorinated water samples (each 100 mL) were collected from 15 WTPs situated along
the Mahaweli river between the Kotmale and Victoria reservoirs. The samples were filtered using
0.22 μm membrane filters to separate bacteria. The retained bacteria were cultured on nutrient
agar plates. The resulting colonies were pooled and underwent DNA extraction. Conventional
PCR was employed with gene-specific primers targeting resistance to five major classes of
antibiotics: β-lactams (bla-TEM), aminoglycosides (aadA1), sulfonamides (sul1, sul2),
tetracyclines (tetM), quinolones (qnrS) and trimethoprim (dfrA14). PCR amplified products were
analyzed for the presence of the expected genes via agarose gel electrophoresis.
Results: The most frequently detected gene was bla-TEM (45.2%), followed by aadA1 (38.1%).
Sul-1 and qnrS were found in 28.6% of the samples. Sul-2 was present in 14.3% of the samples,
while tet-M was detected in 23.8%. The gene dfrA14 was found in 16.7% of the samples. The
tested ARGs were highly abundant at the WTPs located near heavily polluted catchments,
specifically Paradeka (62%), Balagolla (57%), Ulapane (48%), and Greater Kandy (Katugastota)
(48%). Except for the Thalawakelle WTP, where less contaminated raw water from a forested
catchment was used, all other WTPs had at least one tested ARG in their chlorinated water.
Conclusion: Our results revealed the presence of various ARGs in chlorinated drinking water
from WTPs along the Mahaweli river, showing higher abundances associated with the elevated
pollution status of the river catchment.
