Prevalence of antibiotic resistance genes in drinking water of the Kathmandu Valley, Nepal

Abstract

In resource-limited settings, fecal indicator bacterial analysis is the only microbiological water quality test performed, and emerging contaminants, such as antibiotic resistance genes (ARGs), are often neglected. To address this knowledge gap, water samples were collected from shallow wells (n = 24), deep wells (n = 16), stone spouts (n = 14), springs (n = 8), tanker filling stations (TFS; n = 12), water tankers (n = 12), and drinking water treatment plants (DWTPs; n = 6 each of raw and treated water) of the Kathmandu Valley, Nepal, between December 2015 and August 2016 to investigate the presence of five ARGs (blaNDM-1, blaCTX−M, tetB, qnrS, and sul1) and class one integrase gene (intI1). All ARGs were detected in water samples from shallow wells and stone spouts, whereas blaNDM-1 and blaCTX−M were not detected in deep wells and springs. tetB and intI1 were detected at a greater number of water tanker samples than TFS, indicating that water tankers were not disinfected regularly. Only sul1 and intI1 were detected in treated water of DWTPs. Persistence of intI1 throughout the water treatment process and significantly strong correlation (ρ > 0.5, p < 0.05) with the majority of ARGs included in our study suggested the suitability of intI1 to assess the contamination and fate of ARGs in drinking water of the valley. Low free chlorine levels in treated water before pipeline distribution urge water quality managers to evaluate tap water for pathogens and ARGs. Further studies are recommended on emerging contaminants, such as antibiotics, in drinking water sources that are not routinely assessed but can provide selective pressure for the spread of antibiotic resistance in the environment.