Antimicrobial Resistance Profiles of Bacterial Community in Premise Plumbing before and after Water Stagnation

Drinking water stagnation in premise plumbing leads to regrowth of microorganisms, including opportunistic pathogens. Although many studies have evaluated the changes in bacterial community structure, little data are available on the impact of water stagnation on antimicrobial resistance of bacterial communities. In this study, we collected drinking water samples before and after stagnation in premise plumbing in a building. After 24 h of stagnation, an increase in total cell count was observed with a simultaneous decrease in free chlorine residual. Bacterial communities before and after stagnation were incubated with serial dilutions of individual antimicrobial agents (ampicillin, cefotaxime, streptomycin, tetracycline, erythromycin, sulfamethoxazole, chloramphenicol, and ciprofloxacin) in R2A broth for three days to evaluate the antimicrobial resistance profiles. The minimal inhibitory concentrations of the antimicrobial agents against the bacterial communities increased after water stagnation. Community structure analysis revealed that Methylobacterium and Pseudoxanthomonas were dominant in enriched cultures with most antimicrobial agents before and after water stagnation, respectively. These results demonstrate that water stagnation in premise plumbing can affect the antimicrobial resistance profiles of bacterial communities.