In vitro alkaline pH resistance of Enterococcus faecalis.
Enterococcus faecalis is a bacterial species often found in root canals with failed endodontic treatment. Alkaline pastes are widely used in Endodontics because of their biocompatibility and antimicrobial activity, but this microorganism can resist alkalinity. The purpose of this study was to evaluate in vitro the alkaline pH resistance of E. faecalis for different periods up to 14 days. Samples were obtained from the oral cavity of 150 patients from the Endodontic clinic. The pH of the experimental tubes (n=84) was first adjusted with 6M NaOH to pH values of 9.5, 10.5, 11.5 and 12.5 (21 tubes per pH). Twenty clinical isolates and the ATCC 29212 strain were tested. The 5 positive controls and experimental tubes of each pH were inoculated with 10 µL of bacterial suspension and incubated at 36 °C for 24, 48 and 72 h, 7 and 14 days. For each period, the turbidity of the medium was visually compared with a 0.5 McFarland standard. The presence of the microorganism was confirmed by seeding on M-Enterococcus agar. Four tubes containing BHI broth adjusted to the tested pHs were incubated for 14 days to verify if pH changes occurred. The pH of inoculated BHI broth was also measured on day 14 to determine if the microorganism acidified the medium. The growth of all E. faecalis strains occurred at pH 9.5 to 11.5 in all periods. Although turbidity was not observed at pH 12.5, there was growth of 13 and 2 strains at 24 and 48 h, respectively, on M-Enterococcus agar. No tube showed growth at pH 12.5 after 72 h. It was concluded that E. faecalis can survive in highly alkaline pH, and some clinical isolates require 72 h at pH 12.5 to be killed.
Center of Health Sciences, USC - University of Sagrado Coração, BauruSP, Brazil.
Paulo Henrique
PH
Weckwerth
Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, USP - University of São Paulo, BauruSP, Brazil.
Ronald Ordinola
RO
Zapata
Center of Health Sciences, USC - University of Sagrado Coração, BauruSP, Brazil.
Rodrigo Ricci
RR
Vivan
Department of Restorative Dentistry, Araraquara School of Dentistry, UNESP - Univ Estadual Paulista, AraraquaraSP, Brazil.
Mário
M
Tanomaru Filho
Hospital for Rehabilitation of Craniofacial Anomalies (HRAC), USP - University of São Paulo, BauruSP, Brazil.
Amanda Garcia Alves
AG
Maliza
Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, USP - University of São Paulo, BauruSP, Brazil.
Marco Antonio Hungaro
MA
Duarte
D000468:Alkalies / Q000378:metabolism*; D003470:Culture Media; D013293:Enterococcus faecalis / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques
D000468:Alkalies; D003470:Culture Media