Resistance to acidic and alkaline environments in the endodontic pathogen Enterococcus faecalis

K. Nakajo, R. Komori, S. Ishikawa, T. Ueno, Yoichi Suzuki, Y. Iwami, Nobuhiro Takahashi

Research output: Contribution to journalArticlepeer-review

53 Citations (Scopus)


Background/aims: This study aimed to investigate the biochemical mechanisms employed by the endodontic pathogen Enterococcus faecalis to confer acid- and alkali-resistance and to compare these with the mechanisms of representative oral streptococci. Methods: E. faecalis JCM8728, Streptococcus mutans NCTC10449 and Streptococcus sanguinis ATCC10556 were used to assess both acid- and alkali-resistance by examining: (i) growth in complex media; (ii) stability of intracellular pH (pHin); (iii) cell durability to leakage of preloaded BCECF (2′,7′-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein) ; and (iv) cell permeability to SYTOX-Green. Results: Growth was initiated by E. faecalis at pH 4.0-11.0, by S. mutans at pH 4.0-9.0 and by S. sanguinis at pH 5.0-9.0. The pHin was similar to the extracellular pH in S. mutans and S. sanguinis at pH 5-10, while the pHin of E. faecalis was maintained at approximately 7.5-8.5 when extracellular pH was 7.5-10 and was maintained at levels equivalent to the extracellular pH when pH < 7.5. Cell membranes of E. faecalis were resistant to BCECF leakage when extracellular pH was 2.5-12 and to SYTOX-Green permeability at pH 4-10. The cell membrane durability to extracellular pH in E. faecalis was higher than that observed in the Streptococcus strains. Conclusion: Compared to S. mutans, E. faecalis was found to be equally resistant to acid and more resistant to alkalis. The results suggest that pH-resistance in E. faecalis is attributed to membrane durability against acid and alkali, in addition to cell membrane-bound proton-transport systems. These characteristics may account for why E. faecalis is frequently isolated from acidic caries lesions and from persistently infected root canals where calcium hydroxide medication is ineffective.

Original languageEnglish
Pages (from-to)283-288
Number of pages6
JournalOral Microbiology and Immunology
Issue number5
Publication statusPublished - 2006 Oct 1


  • Acid-resistance
  • Alkali-resistance
  • Endodontic pathogen
  • Enterococcus faecalis

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Dentistry(all)
  • Microbiology (medical)


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