Biofilm removal in hospital sink drains drives unintended surges in antibiotic resistance.

The prevalence and proliferation of antimicrobial-resistant bacteria is considered one of the critical issues of our time. Wastewater is a habitat for complex microbial communities where bacteria share antimicrobial-resistance genes through horizontal gene transfer. Hospital wastewater plumbing systems are an ideal reservoir for environmental and pathogenic bacteria to interface and exchange antimicrobial-resistance genes. Replacement of contaminated plumbing may be the most intuitive and widely deployed response to the detection and colonization of highly-resistant potentially pathogenic bacteria in hospital sink drains. In this study, we analyzed sink-drain biofilms from six intensive-care patient rooms using shotgun metagenomic sequencing and microbial culture. We show an evident shift in biofilm community structure toward increased abundance of Enterobacteriaceae following plumbing replacement. Higher resistome load and abundance of clinically relevant resistance and typically encountered mobile genes in the newly replaced plumbing was also observed. Taken together, these finding suggest that exchanging contaminated plumbing for new plumbing may actually have the unexpected consequence of increased abundance of Enterobacterales and antimicrobial-resistance genes in the sink drains. Disruption of preexisting complex environmental biofilms may result in an unintended microbial population shifts and a potential subsequent increase in the amount of antimicrobial-resistant Enterobacterales which are targeted for elimination.