Antimicrobial susceptibility and molecular analysis of Enterococcus faecalis originating from endodontic infections in Finland and Lithuania

Background/aims: Enterococcus faecalis strains with multiple antibiotic resistances can cause infections that are difficult to treat. The microbial flora in treatment-resistant apical periodontitis is dominated by E. faecalis, and is a potential source of infections at other sites. Material and methods: Sensitivities to a range of antibiotics were determined for 59 endodontic E. faecalis isolates from Finland and Lithuania. The DNA sequence of the gene responsible for the species' intrinsic quinupristin-dalfopristin resistance, lsa, was determined from two isolates with diminished resistance. Four pairs of isolates from the same root canal were typed by pulsed-field gel electrophoresis. Results: A high prevalence of resistance to rifampicin was found, whereas all isolates were susceptible or showed intermediate susceptibility to penicillin and ampicillin and four isolates were unusually susceptible to cefotaxime. No vancomycin or high-level gentamicin resistance was detected. Nine of 59 isolates were susceptible to quinupristin-dalfopristin. A fully quinupristin-dalfopristin-susceptible isolate also susceptible to clindamycin produced a truncated Lsa polypeptide, and an isolate with borderline quinupristin-dalfopristin-susceptibility had mutations proximal to the predicted ribosomal binding site. Pulsed-field gel electrophoresis showed that the same root canal could harbor two different strains of E. faecalis during the course of the same infection. Conclusion: Despite the differing antibiotic usage in Finland and Lithuania, E. faecalis from endodontic infections in these countries showed similar susceptibility patterns with levels of resistance considered typical for the species, and decreased resistance to clindamycin and quinupristin-dalfopristin as well as lesions in the lsa gene which were similar to those described in other clinical isolates.