Methylparaben as an environmental contaminant modulating virulence traits in waterborne bacteria.

Methylparaben (MP), a preservative found in daily-use products, can reach drinking water (DW) due to its incomplete removal in water treatment plants. Although parabens are related to endocrine disruption, their effects on bacterial virulence as environmental contaminants remain to be understood. This study investigates the effect of MP at environmental concentrations (15 μg/L) on the virulence of planktonic and biofilm cells of Acinetobacter calcoaceticus and Stenotrophomonas maltophilia isolated from a drinking water distribution system. The impact of MP on bacterial growth and outer membrane vesicles (OMVs) release was assessed, including the size of OMVs and lipid and protein content. The ability of MP-exposed and non-exposed bacterial cells to form biofilms and the potential to invade human gingival fibroblasts (HGF) were also studied. The exposure to MP causes more changes in S. maltophilia OMVs than in A. calcoaceticus. Increased lipid content in MP-exposed S. maltophilia biofilm-derived OMVs was observed. However, a lower concentration of OMVs and lipid content was found in S. maltophilia planktonic cells. The OMVs produced by MP-exposed biofilm-derived cells of A. calcoaceticus had a larger hydrodynamic diameter (Dₕ), whereas those from planktonic cells had a smaller Dₕ compared to the controls. Enhanced biofilm formation was found for both MP-exposed bacteria, and MP-exposed A. calcoaceticus planktonic cells showed a heightened ability to invade HGF, resulting in higher intracellular bacterial counts and increased replication. The overall findings underscore the impact of MP on DW bacteria, suggesting that MP can amplify interconnected bacterial virulence mechanisms, raising potential public health concerns.