Molecular identification of microorganisms from endodontic infections

A relatively wide range of bacteria have been isolated from root canals usi ng standard culture techniques. However, only 50% of the bacteria in the or al cavity are cultivable (S. S. Socransky et al., Arch. Oral Biol. 8:278-28 0, 1963); hence, bacterial diversity in endodontic infections is underestim ated. This study used a PCR-based 16S rRNA gene assay, followed by cloning and sequencing of 16S rRNA amplicons from a small subset of samples to asse ss the diversity of bacteria present in infected root canals. A total of 41 clinical samples from 15 de novo and 26 refractory cases of endodontic inf ections were assessed. Of these samples, 44% were positive by culture and 6 8% were positive by PCR. Eight samples were selected for further analysis. Of these, the two de novo cases yielded sequences related to those of the g enera Enterococcus, Lactobacillus, Propionibacterium, and Streptococcus, an d two clones were related to previously uncultivated bacteria, while the si nus-associated, de novo case yielded sequences related to those of the gene ra Lactobacillus, Pantoea, Prevotella, and Selenomonas. The five refractory cases produced clones which were related to the genera Capnocytophaga, Cyt ophaga, Dialister, Eubacterium, Fusobacterium, Gemella, Mogibacterium, Pept ostreptococcus, Prevotella, Propionibacterium, Selenomonas, Solobacterium, Streptococcus, and Veillonella and two clones representing previously uncul tivated bacteria. The phylogenetic positions of several clones associated w ith the Clostridiaceae and Sporomusa subgroups of the Firmicutes grouping a re also shown. This study demonstrates that molecular techniques can detect the presence of bacteria in endodontic infections when culture techniques yield a negative result and can be used to identify a wider range of endodo ntic-infection-related bacteria including the presence of previously uniden tified or unculturable bacteria.