Impact of chlorinated methylparaben derivatives on drinking water biofilm structure and antibiotic susceptibility

Chlorination is a disinfection strategy widely used in drinking water distribution systems that can lead to the formation of harmful disinfection by-products. Parabens, a class of emerging contaminants, can react with chlorine and form parabens transformation products (PTP). This study investigates the formation and biological impact of PTP resulting from the chlorination of methylparaben (MP) with free chlorine. Both mono-chlorinated MP (3-Cl-MP) and di-chlorinated MP (3,5-diCl-MP) were produced and the characteristics of 7-days-old dual-species biofilms of Acinetobacter calcoaceticus and Stenotrophomonas maltophilia exposed to these PTP were assessed. Although 3,5-diCl-MP reduced bacterial culturability, 3-Cl-MP and 3,5-diCl-MP exposure increased the number of viable but non-culturable (VBNC) cells of A. calcoaceticus from dual-species biofilms by 3- and 5-fold, respectively. Exposure to 3-Cl-MP also increased VBNC cells in dual-species biofilms and the biofilm thickness by 10 μm. Extracellular polymeric substances showed a 2-fold increase in polysaccharide content upon exposure to both PTP. Interestingly, while MP exposure increased bacterial tolerance to chlorine, PTP exposure enhanced susceptibility. Biofilms exposed to PTP showed higher reductions in total and culturable cells, increased numbers of cells with damaged membranes, and improved chlorine efficacy in reducing the biofilm extracellular protein and thickness. Furthermore, 3,5-diCl-MP exposure increased S. maltophilia susceptibility to minocycline and trimethoprim-sulfamethoxazole. These findings demonstrate the complex effects of PTP on DW biofilms and highlight the need to evaluate conventional disinfection strategies to protect DW from the impact of parabens and their chlorinated by-products. • MP-chlorinated by-products change DW biofilms characteristics and structure. • MP-chlorinated by-products increase VBNC cells in exposed biofilms. • 3-Cl-MP and 3,5-diCl-MP-exposure increase polysaccharide content in EPS matrix. • MP-chlorinated by-products increase bacterial susceptibility to chlorine. • 3,5-diCl-MP increased S. maltophilia cells susceptibility to MINO and TMP-SMX.