Quaternary Ammonium Compounds Inhibit Enterococcus faecalis Biofilms.

Objectives: Enterococcus faecalis forms robust biofilms that survive harsh conditions and are able to tolerate antimicrobials. There is a constant search for more effective antimicrobial compounds that can inhibit biofilm formation by this pathogen. The study objective was to investigate the effect of two quaternary ammonium compounds (QACs) namely benzalkonium chloride (BAC) and cetylpyridinium chloride (CPC) on E. faecalis biofilms in vitro.
Methods: The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC), minimum biofilm eradication concentration (MBEC) of the 2 QACs against E. faecalis were determined using standard microbiological assays. The biofilm architecture and cell viability of biofilms grown in the presence of the QACs on hydroxyapatite discs were investigated using confocal laser scanning microscopy (CLSM).
Results: The MIC and MBIC for both the compounds were found to be 4 μg/mL, showing that biofilm inhibition accompanied growth inhibition when E. faecalis was treated with these compounds. The biofilms (72h) were eradicated by 40 μg/mL for both compounds. Confocal microscopic imaging confirmed the lack of an organized biofilm mass and that the cells remained as planktonic isolates on the hydroxyapatite discs.
Conclusions: The results of our study highlight that the QACs tested, demonstrate antibiofilm properties against E. faecalis, indicating the potential for development of novel antibiofilm compounds.