title: Assessment of dentinal tubule invasion capacity of Enterococcus faecalis under stress conditions ex vivo.
abstract: OBJECTIVE
  To investigate the dentinal tubule invasion capacity of Enterococcus faecalis under alkaline and energy starvation stress conditions.
  
  
  METHODS
  The root canals from human single-rooted teeth (n = 40) were infected with E. faecalis under alkaline (pH 9, 10, 11 and 12) and energy starvation (no glucose, 0.05% glucose and 0.15% glucose) stress conditions. The root canals were prepared in a standard manner and treated to remove the smear layer before incubation. After 4 weeks of cultivation, the roots were split vertically into two halves: one half was processed for biofilm formation analysis using a scanning electron microscope; the other half was stained with fluorescent DNA-binding reagents, washed thoroughly and sectioned (100 μm thick), and the depth of tubule invasion by the microorganism was examined by confocal laser-scanning microscopy. The extent of dentine tubule invasion was analysed statistically.
  
  
  RESULTS
  The E. faecalis strain resulted in biofilm formation and dentine tubules invasion under all of the stress conditions, except for pH 11 and 12 conditions. However, the tubule penetration distance was markedly reduced in these stress conditions (P < 0.01) compared with in tryptic soy broth (TSB) or pH 7 medium. The invasion depth in the middle root dentine was significantly higher than in the apical sections in TSB and energy starvation medium (P < 0.01).
  
  
  CONCLUSIONS
  Ex vivo E. faecalis formed biofilms and colonized dentine under alkaline and glucose starvation stress conditions, but its ability to invade dentine tubules was significantly decreased.
authors.affiliation: Department of Endodontics and Operative Dentistry, Shanghai Key Laboratory of Stomatology, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: S
authors.initials: S
authors.lastname: Ran
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: W
authors.initials: W
authors.lastname: Jiang
authors.forename: C
authors.initials: C
authors.lastname: Zhu
authors.forename: J
authors.initials: J
authors.lastname: Liang
mesh_terms: D018441:Biofilms; D003804:Dentin / Q000382:microbiology*; D013293:Enterococcus faecalis / Q000472:pathogenicity* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D013312:Stress, Physiological
keywords: CLSM; Enterococcus faecalis; biofilms; dentinal tubules invasion; stress conditions