Identification of Enterococcci isolated from canals of root filled teeth with periapical lesions and their antimicrobial susceptibility to different antibiotics

Abstract

Aim The objective of the present study was to investigate the occurrence of Enterococcus spp. in root filled teeth with periapical lesions and the in vitro antimicrobial susceptibility of the isolates.Methodology Sixty teeth with failed root canal treatment were included in the study. During nonsurgical endodontic retreatment, the root filling material was removed and the canals were sampled and microbiologically examined. Enterococcus ssp. isolates were tested for their antibiotic susceptibilities using the E‐test system (AB BIODISK, Solna, Sweden). The following antibiotics were used: benzylpenicillin, amoxicillin, amoxicillin‐clavulanic acid, erythromycin, azithromycin, vancomycin, chloramphenicol, tetracycline, doxycycline, ciprofloxacin and moxifloxacin. The strains were also tested for β‐lactamase production with nitrocefin (Oxoid, Hampshire, England).Results Microorganisms were recovered from 51 of 60 teeth. Enterococcus faecalis was recovered from 27 of the 51 canals with bacteria, 18 times in pure culture. All strains were susceptible to penicillins; however, the MICs of amoxicillin and amoxicillin‐clavulanic acid (MIC90 = 0.75 µg mL−1) were lower than that for benzylpenicillin (MIC90 = 3.0 µg mL−1). All strains studied were also susceptible to vancomycin and moxifloxacin, while 95.2% were susceptible to chloramphenicol. Among the isolates, 85.7% were susceptible to tetracycline and doxycycline, and 80.9% to ciprofloxacin. The MIC of erythromycin ranged from 0.38 to >256 µg mL−1; only 28.5% of the strains were susceptible (MIC ≤ 0.5 µg mL−1). Limited susceptibility was also observed with azithromycin, which was active against only 14.2% of isolates. No strains produced β‐lactamase.Conclusions Enterococcus faecalis was present in a large number of canals in teeth with failed root fillings and were completely susceptible, in vitro, to amoxicillin, amoxicillin‐clavulanic acid, vancomycin and moxifloxacin. Most isolates were susceptible to chloramphenicol, tetracycline, doxycycline or ciprofloxacin. Erythromycin and azithromycin were least effective. (Supported by the Brazilian agencies FAPESP 00/13686‐8, 00/13689‐7; CNPq 520277/99‐6 and CAPES BEX2449/02‐1).