title: Antimicrobial activity of varying concentrations of sodium hypochlorite on the endodontic microorganisms Actinomyces israelii, A. naeslundii, Candida albicans and Enterococcus faecalis.
abstract: OBJECTIVE
  To determine the resistance of microorganisms associated with refractory endodontic infections to sodium hypochlorite used as a root canal irrigant.
  
  
  METHODS
  Two strains each of Actinomyces naeslundii, Candida albicans and Enterococcus faecalis were tested as late logarithmic phase inocula, against sodium hypochlorite adjusted to 0.5, 1.0, 2.5 and 5.25% w/v. Contact times used were 0, 10, 20, 30, 60 and 120 s. In the case of E. faecalis, additional experiments used contact times of 1.0, 2.0, 5.0, 10.0 and 30.0 min. Anti-microbial action was halted by sodium thiosulphate addition. Survivors were measured primarily using viable counts on drop plates. Additionally, pour plates were used to count low colony-forming units (cfu) and dilutions to 10(-6) were used to count high cfu.
  
  
  RESULTS
  All concentrations of NaOCl lowered cfu below the limit of detection after 10 s in the case of A. naeslundii and C. albicans. However, E. faecalis proved to be more resistant to NaOCl. Using 0.5% NaOCl for 30 min reduced cfu to zero for both strains tested. This compares with 10 min for 1.0%, 5 min for 2.5% and 2 min for 5.25% (P < 0.001). Regression analysis for the dependent variable log(e)(count + 1) with log(e)(time + 1) and concentration as explanatory variables gave rise to a significant interaction between time and concentration (P < 0.001).
  
  
  CONCLUSIONS
  The published association of E. faecalis with refractory endodontic infection may result, at least partially, from high resistance of this species to NaOCl. This does not appear to be the case with A. naeslundii or C. albicans.
authors.affiliation: Oral Microbiology Laboratory, University Dental Hospital of Manchester, Manchester, UK.
authors.forename: C E
authors.initials: CE
authors.lastname: Radcliffe
authors.forename: L
authors.initials: L
authors.lastname: Potouridou
authors.forename: R
authors.initials: R
authors.lastname: Qureshi
authors.forename: N
authors.initials: N
authors.lastname: Habahbeh
authors.forename: A
authors.initials: A
authors.lastname: Qualtrough
authors.forename: H
authors.initials: H
authors.lastname: Worthington
authors.forename: D B
authors.initials: DB
authors.lastname: Drucker
mesh_terms: D000190:Actinomyces / Q000187:drug effects*; D002176:Candida albicans / Q000187:drug effects*; D015169:Colony Count, Microbial; D003786:Dental Pulp Cavity / Q000382:microbiology; D013293:Enterococcus faecalis / Q000187:drug effects*; D016014:Linear Models; D008826:Microbial Sensitivity Tests; D012388:Root Canal Irrigants / Q000008:administration & dosage*; D012973:Sodium Hypochlorite / Q000008:administration & dosage*
chemical_list: D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite