Impact of Chlorine Treatment on Antibiotic Resistance Pattern of Coliforms in Drinking Water Supplied in Kathmandu Valley

Abstract

Chlorine is the most widely used disinfectant for treating drinking water. However, some evidences suggest that it leads to bacterial resistance to different antibiotics. A descriptive cross-sectional study was conducted from the duration of June 2023 to May 2024 with the primary aim of determining the antibiotic resistance patterns in coliforms isolated from water before and after chlorine treatment. The chlorine resistance was also studied in the isolated coliforms. A total of 60 (26 untreated and 34 treated) water samples were processed for the isolation of total coliforms by the membrane filtration technique, and the isolates were identified from morphological and biochemical characteristics. Antibiotic resistance patterns of the coliforms were obtained by performing antibiotic susceptibility tests using the Kirby-Bauer disc diffusion method. Additionally, the isolates were exposed to various concentrations of chlorine for 10 minutes, 20 minutes, and 30 minutes to detect chlorine resistance in coliforms. Of all the water samples tested, 50 (83.3%) samples contained coliforms. Coliform detection was greater in untreated (96.1%) than in treated (73.5%) samples. The number of total coliforms in untreated samples was higher (0 to 1160 CFU/100 mL) than in treated samples (0 to 328 CFU/100 mL). In this study, Klebsiella spp. (13 from untreated and 8 from treated samples) and E. coli (13 from untreated and 19 from treated samples) were isolated. Antibiotic susceptibility test of the coliforms revealed that 50% of the Klebsiella spp. and 36.8% of E. coli isolated from treated water, whereas 69.2% of Klebsiella and 53.8% of E. coli from untreated water were resistant to ceftriaxone. Upon exposure of coliforms to chlorine for different time periods, 4, 2, and 1 coliform obtained from treated water showed growth in 50 ppm chlorine concentration in 10 min, 20 min, and 30 min, respectively, whereas 3, 2, and 1 coliform bacteria from untreated water showed growth at 50 ppm in 10 min, 20 min and 30 min respectively. This study could not show the impact of chlorine treatment on the antibiotic resistance of coliforms. However, continuous monitoring might be necessary to determine the cause of the spread of antibiotic resistance in bacteria.

Stam. J. Microbiol. 2025;15(1):69-74