Effects of prolonged exposure to alkaline pH on Enterococcus faecalis survival and specific gene transcripts

Introduction: The persistence of Enterococcus faecalis in treated root canals has been attributed to its resistance to the high pH of antimicrobial agents used during treatment, but the specific mechanisms are not clear. We investigated the survival and gene expression of E. faecalis maintained in alkaline media. Methods: E. faecalis JH2-2 was maintained in media at pH 7, 10, 11 and 12 at either 25°C or 37°C for 1 week (168 h). At 24, 48, 72, 120 and 168 h, cell viability was determined in parallel with real-time quantitative polymerase chain reaction analyses of stress response genes (dnaK, fba, ftsZ, GroEL, napA, pbp5, tsf and tuf). Results: After 1 week the E. faecalis showed survival levels of 100% in pH 7, 1% in pH 10, 0.001% in pH 11 and 0.00001% in pH 12 media. At 37°C increased levels of gene transcripts occurred between 72 and 120 h in pH 7 media for ftsZ and dnaK, and in pH 10 media for ftsZ, pbp5, dnaK, napA, tsf, fba and GroEL. No increase in transcripts was observed at 37°C in media at pH 11 or pH 12, nor at 25°C in any media. Conclusion: Transcripts of ftsZ, a gene involved in cell division, increased by 37-fold after 120 h at pH 10 at 37°C. Overall, the greatest increase in levels of gene transcripts occurred in cultures maintained in pH 10 media at 37°C. These data may assist in understanding the survival strategies of E. faecalis following prolonged exposure to alkaline pH levels.