Sub-MIC of sulfamethoxazole on antibiotic resistance in drinking water biofilms

The ingestion of water from a drinking water distribution system (DWDS) is a potential pathway for human exposure to active antibiotic resistance genes (ARGs). DWDS biofilms are a critical reservoir of ARGs as they are continually exposed to environmental stressors, such as sub-minimum inhibitory concentrations (sub-MICs) of antibiotics, which pose a risk of ARG dissemination into bulk water. The aim of this study was to investigate associations between sulfamethoxazole exposure and ARG abundance, ARG expression, and antibiotic-resistant bacteria (ARB) in drinking water biofilms adhered to distribution pipe walls. The ARGs intI1, sul1, and sul2 were detected through qPCR and RT-qPCR in both the biofilm and the bulk water. A significant positive correlation was found between sulfamethoxazole presence and promotion of intI1, suggesting that it is associated with ARG propagation. This was further supported by the observed co-occurrence between intI1 and sul2. ARGs found in the biofilm were correlated with ARGs in the bulk water; however, this relationship was not statistically significant. Low-abundance genera in the biofilm were found to significantly correlate with intI1, which has been established to be a marker of anthropogenic pollution and horizontal gene transfer. These findings highlight the association between DWDS biofilms and ARG dynamics under antibiotic exposure and warrant further investigation into their potential role in wider resistance dissemination.