Fate of the resistance profile of drinking water biofilm exposed to a sub-minimum inhibitory concentration of ciprofloxacin

Early research shows that biofilms in drinking water systems—such as those in pipes and filtration beds—can promote antimicrobial resistance (AMR). This study examined how low levels of the antibiotic ciprofloxacin affect multi-species biofilms in PVC pipes. Exposure to sub-inhibitory antibiotic concentrations increased total bacterial cell counts, suggesting stimulation of AMR-related responses. The biofilms were highly diverse, but changes in community composition were linked to key resistance genes (e.g., intI1 and sul1). Notably, certain low-abundance bacteria, such as Asinibacterium, may play a disproportionate role in spreading resistance genes. The findings underscore that even low antibiotic residues in drinking water systems can influence biofilm dynamics and enhance AMR risk, highlighting the need for targeted control strategies.