Increase in anthropogenic antibiotic resistance markers in water supplied by an overhead tank based-water distribution system

Abstract

Overhead tank (OHT)-based gravity-fed water distribution systems are popular in many low and middle-income countries; yet, they are poorly characterized despite being notorious for water quality deterioration. We investigated the potential for antibiotic resistance and horizontal gene transfer in tap water as it traversed through a gravity-fed water distribution system with six interconnected OHTs. Tap water was sampled from nine buildings over three seasons (summer, monsoon and winter) to compare the water quality in OHTs vs. at the user-end. Antibiotic resistance genes (ARGs) (sul1, sul2, blaOXA-1, and ermF), class 1 integron-integrase gene (intI1), opportunistic pathogens (Legionella pneumophila and Mycobacterium avium), 16S rRNA gene copies, yccT (Escherichia coli) and water quality parameters were characterized. Tap water samples at the user-end indicated selection of intI1, which correlated with the levels of 16S rRNA gene copies (r = 0.79), sul1 (r = 0.77), Cu (r = 0.48) and nitrate (r = 0.28). The absolute levels of sul1, intI1, opportunistic pathogens, 16S rRNA gene copies, and heavy metals were generally higher at the user-end and during the warmer seasons. The tap water was highly corrosive and levels of Fe and Pb exceeded the WHO guidelines in 24/81 and 19/81 samples, respectively. Heavy metals, DWDS-specific factors, season of sampling, and nitrate correlated with the levels of sul1, intI1, and opportunistic pathogens in tap water at the user-end. The findings of this study expose the susceptibility of OHTs to selection of intI1 and suggest control of corrosion to limit the prevalence and levels of ARGs and opportunistic pathogens in tap water.