Biofilm dispersion is a survival mechanism where bacteria transition to a planktonic lifestyle. Dispersion is not characterized in Enterococcus faecalis (E. faecalis), a human intestinal tract bacterium. In semi-batch culture experiments, we determined steady state biofilms formed after 48 hours when E. faecalis was grown in 10% Tryptic Soy Broth (TSB) at 37oC without shaking. Next, we challenged biofilm cultures with a 10-fold step increase in nutrients after 4 days of growth to avoid interference from self-induced dispersion and found a statistically significant dispersion response. To evaluate the effect of bile acids on nutrient-induced dispersion, we exposed dispersed cells to the primary bile acid cholic acid or the secondary bile acid lithocholic acid. Lithocholic acid retained biofilm growth during nutrient-induced dispersion and thus may cause increased biofilm formation and preservation in the gut. To evaluate E. faecalis antibiotic tolerance, we conducted dose finding assays with the oxazolidinone linezolid and glycopeptide vancomycin. Mid-log cultures were grown for 18 hours in 100% TSB and shaken prior to treatment. E. faecalis displayed antibiotic tolerance when treated with 50 µg/ml of linezolid, resulting in a 0.5 log reduction. Our study has revealed novel findings on the growth and dispersion response of E. faecalis biofilms.
