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Introduction: The aim of this study was to evaluate susceptibility of predominant endodontic pathogens isolated from teeth with symptomatic apical periodontitis to most commonly prescribed antibiotics. Methods: Among 58 patients with symptomatic apical periodontitis, 47 and 11 cases were caused by primary and secondary root canal infection, respectively. The microbial samples were taken either from the root canals (35 cases) or by aspiration from apical abscesses (23 cases). Culture methods were used to identify the microorganisms present in the samples. Antibiotic susceptibilities of all isolates were evaluated by using the E-test method. Results: Microorganisms were isolated from 49 of the 58 samples studied and included facultative and obligate anaerobes. Streptococci and obligate anaerobes were the predominant microorganisms in cases of primary infection. Enterococcus faecalis dominated in cases of secondary infection. All tested microorganisms were highly sensitive to penicillin G, amoxicillin, and ampicillin. Susceptibilities to clindamycin and erythromycin were 73.8% and 54.7%, respectively. About 40% of the isolates were resistant to tetracycline. Morethan50% ofall anaerobes wereresistant to metronidazole. All E. faecalis isolates were resistant to clindamycin. Conclusions: Based on the study results, penicillin and amoxicillin are suitable antibiotics for treatment of endodontic infection when conventional root canal treatment alone is insufficient. Clindamycin could be advised for penicillin-allergic patients with primary endodontic infections. (J Endod 2010;-:1‐6)

The occurrence of Enterococcus faecalis in root canals of previously root filled teeth with apical periodontitis requiring retreatment was studied in Lithuanian patients. Twenty-five asymptomatic teeth were included in the study. Avoiding contamination microbiological samples were taken from the canals before and after preparation and irrigation with sodium hypochlorite and EDTA. Microbes were isolated from 20 of 25 teeth. E. faecalis was isolated from 14 of those 20 culture positive teeth, usually in pure culture or as a major component of the flora. Second samples taken after preparation revealed growth in 7 of the 20 teeth. Five of the seven cases were E. faecalis in pure culture. Isolation of E. faecalis was not related to the use of any particular root filling material in the original root filling. The results indicate that, rather than previous chemical treatment, it is the ecological conditions present in the incompletely filled root canal that are important for the presence of E. faecalis in these teeth.