Prevalence of antimicrobial resistance in a Bulgarian drinking water supply system

Drinking water quality and safety are of great concern for public health. The aim of this study was to assess the prevalence of antimicrobial resistance (AMR) among the heterotrophic bacteria in drinking water provided by a Bulgarian drinking water supply system (DWSS). Culture-dependent methods and conventional PCR assays were used to study drinking water sampled from six locations on its way from the water source to the consumers' taps. The populations of bacteria resistant to nine antibiotics (ABs) from different classes were quantified and the occurrence of seven antibiotic resistance genes (ARG) was determined. The species composition of the bacterial community and the AMR phenotype of isolated bacteria were determined. The AMR level underwent changes within the DWSS network and the population's proportion of bacteria resistant towards the tested ABs differed depending on the sampling site. The increased level of resistance towards some ABs in drinking water emphasize the role of DWSS as a reservoir of antibiotic-resistant bacteria (ARB) and ARGs that could pose a potential human health risk. Being focused on a Bulgarian DWSS, our study will contribute to establishing health hazards associated with ARB and ARGs in drinking water.