Dentin tubule invasion by Enterococcus faecalis under stress conditions ex vivo

Enterococcus faecalis is the species most frequently isolated from failed endodontic treatments because it can survive under stress conditions imposed by root canal treatment. The objective of this study was to determine the ability of E. faecalis to invade dentine tubules under alkaline and energy-starvation stress and to explore the potential mechanisms. Roots from single-rooted human teeth were infected with E. faecalis under alkaline and energy-starvation stress conditions. After 4 wk of culture, samples were processed to establish the tubule-penetration distance. In addition, the hydrophobicity of E. faecalis cells under these conditions was analysed and the expression of genes involved in adhesion was quantified by real-time quantitative PCR. Culture of E. faecalis under alkaline and energy-starvation stress conditions resulted in a marked reduction of tubule-penetration distance, a significant increase in hydrophobicity of the bacterial surface, and marked down-regulation of most adhesin genes compared with E. faecalis cultured in tryptic soy broth. The results indicate that the dentine tubule invasion ability of E. faecalis was markedly decreased under alkaline and glucose-starvation stress conditions, possibly because of the increase of hydrophobicity and down-regulation of some adhesion genes.