Inhibition of biofilm formation and exopolysaccharide synthesis of Enterococcus faecalis by phenyllactic acid

This study aimed to evaluate the inhibitory activity of phenyllactic acid (PLA) against the biofilm formation of Enterococcus faecalis and to explore its potential molecular mechanism. The MIC value of PLA that inhibited the growth of E. faecalis R612-Z1 in BHI broth was 5 mg/mL. PLAs at subinhibitory concentrations of 1.25 and 2.50 mg/mL were found to inhibit biofilm formation by a crystal violet staining assay. The cell swimming and swarming motilities of E. faecalis were reduced in the presence of PLA. An apparent decrease in the thickness of PLA-treated biofilms was observed through confocal laser scanning microscopy analysis. The exopolysaccharide production in E. faecalis biofilms was inhibited by EPS quantification assay and scanning electron microscopy (SEM). qRT-PCR analyses showed that PLA down-regulated the transcription of Ebp pili genes (ebpABC) and Epa polysaccharide genes (epaABE). PLA inhibited the biofilm formation by interfering with cell mobility and EPS production of E. faecalis. In addition, PLA at concentrations of 10.0 mg/mL can effectively control the bacterial cells in a three-day-old mature biofilm of E. faecalis grown on 24-well flat-bottom polystyrene plates and stainless-steel surfaces. Thus, PLA is potentially an effective agent to control E. faecalis biofilms.