Mechanisms involved in the resistance of Enterococcus faecalis to calcium hydroxide

AIM: This study sought to clarify the mechanisms that enable E. faecalis to survive the high pH of calcium hydroxide. METHODOLOGY: E. faecalis strain JH2-2 was exposed to sublethal concentrations of calcium hydroxide, with and without various pretreatments. Blocking agents were added to determine the role of stress-induced protein synthesis and the cell wall-associated proton pump. RESULTS: E. faecalis was resistant to calcium hydroxide at a pH of 11.1, but not pH 11.5. Pre-treatment with calcium hydroxide pH 10.3 induced no tolerance to further exposure at pH 11.5. No difference in cell survival was observed when protein synthesis was blocked during stress induction, however, addition of a proton pump inhibitor resulted in a dramatic reduction of cell viability of E. faecalis in calcium hydroxide. CONCLUSIONS: Survival of E. faecalis in calcium hydroxide appears to be unrelated to stress induced protein synthesis, but a functioning proton pump is critical for survival of E. faecalis at high pH.