Parabens at Environmental Levels Modulate Virulence and Antimicrobial Tolerance of Exposed Biofilm Cells

Background/Objectives: Parabens are widely used preservatives detected at trace levels in drinking water. Although their endocrine-disrupting effects are well established, their long-term impact on environmental bacteria remains poorly understood. This study investigated the effects of parabens on changes in bacterial phenotypic virulence traits and antimicrobial tolerance of bacteria within drinking water biofilms. Methods: Acinetobacter calcoaceticus and Stenotrophomonas maltophilia biofilms were grown on polyvinyl chloride coupons for 26 days under exposure to methyl- (MP), propyl- (PP), butyl-paraben (BP), or a paraben mixture (MIX) at 0.15 µg/L. Biofilm regrowth and virulence-associated traits, including motility (swimming, swarming, and twitching), extracellular enzymes (gelatinase, protease, and lipase), and siderophore production, were evaluated. The effect of prolonged MP exposure (10 weeks) on antimicrobial tolerance was assessed. Results: In A. calcoaceticus, MP reduced biofilm biomass by 32%, whereas MIX increased biomass by 25% and culturability (1.1-fold). S. maltophilia showed increased biofilm culturability with PP (50%), and increased biomass of 2.6-, 2.4-, and 1.8-fold for PP, BP, and MIX, respectively. Biofilm cells exhibited higher virulence factor production than planktonic counterparts. S. maltophilia biofilm cells exposed to BP and MIX showed enhanced swimming and swarming motility, with halo diameters up to fivefold larger than controls. Lipase production increased under BP and MIX exposure, whereas MP exposure reduced it. A MP-induced reduction in motility was observed for A. calcoaceticus and S. maltophilia. Long-term MP exposure results in reduced susceptibility to ceftazidime and minocycline in A. calcoaceticus. Conclusions: Environmentally relevant concentrations of parabens can modulate bacterial virulence traits, increasing biofilm formation, motility and lipase production, and antimicrobial tolerance.