title: Isolation of alkaline-tolerant bacteria from primary infected root canals.
abstract: BACKGROUND
  Alkaline-tolerant bacteria in primary infected root canals could have enhanced survival capacity against antimicrobials commonly used in root canal treatment. The aims of this study were to isolate and characterize alkaline-tolerant bacteria before endodontic treatment (S1), after chemomechanical root canal preparation (S2), and after calcium hydroxide dressing (S3).
  
  
  METHODS
  Bacteriologic samples were obtained from 43 primary infected root canals. Samples were inoculated into culture media at a pH of 9 and incubated anaerobically. The identities of bacterial isolates were determined by 16S ribosomal RNA sequencing.
  
  
  RESULTS
  All S1 samples were culture positive, with 70% harboring bacteria tolerating a pH of 9. Gram-positive bacteria Pseudoramibacter alactolyticus and Streptococcus spp were the most frequently isolated strains with a prevalence of 54%. Of 13 culture-positive S2 samples, 8 isolates tolerated a pH of 9, namely Streptococcus sanguinis, Enterococcus faecalis, Enterobacter cancerogenus, Streptococcus oralis, and Fusobacterium nucleatum. Seven of these 8 isolates (88%) were correspondingly isolated at S1. All 3 culture-positive S3 samples tolerated a pH of 9, namely S. sanguinis and E. faecalis, which were also isolated in the corresponding S1 and S2 samples.
  
  
  CONCLUSIONS
  We showed that the presence of alkaline-tolerant Streptococcus and Enterococcus spp in primary infected root canals could lead to their persistence during and after root canal treatment and could pose a challenge to current treatment efficacy.
authors: Faculty of Dentistry, National University of Singapore, Singapore, Singapore; National Dental Center, Singapore, Singapore.
authors: Hui Pau
authors: HP
authors: Lew
authors: Faculty of Dentistry, National University of Singapore, Singapore, Singapore.
authors: Samantha Yiling
authors: SY
authors: Quah
authors: National Dental Center, Singapore, Singapore.
authors: Jeen Nee
authors: JN
authors: Lui
authors: The Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden.
authors: Gunnar
authors: G
authors: Bergenholtz
authors: Faculty of Dentistry, National University of Singapore, Singapore, Singapore.
authors: Victoria Soo
authors: VS
authors: Hoon Yu
authors: Faculty of Dentistry, National University of Singapore, Singapore, Singapore. Electronic address: denkst@nus.edu.sg.
authors: Kai Soo
authors: KS
authors: Tan
mesh_terms: D001419:Bacteria / Q000302:isolation & purification*; D001424:Bacterial Infections / Q000382:microbiology*; D003786:Dental Pulp Cavity / Q000382:microbiology*; D003788:Dental Pulp Diseases / Q000382:microbiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration
keywords: Alkaline-tolerant bacteria; endodontic treatment; root canal infection