Molecular analysis of the root canal microbiota associated with endodontic treatment failures

Introduction:  The failure of endodontic treatment is usually caused by persistent/secondary intraradicular infections and Enterococcus faecalis has been considered to be the main pathogen involved. Nevertheless, the breadth of bacterial diversity involved with endodontic treatment failures remains to be consistently explored by culture-independent approaches.
Methods:  This study determined the intraradicular microbiota of root-canal-treated teeth with post-treatment apical periodontitis using 16S ribosomal RNA gene clone library analysis.
Results:  Bacteria were present in all cases, confirming the infectious etiology of post-treatment disease. Seventy-four bacterial taxa belonging to six phyla were found in the nine cases investigated. Of these, 55% were identified as as-yet-uncultivated phylotypes, which also made up a significant proportion of the microbiota in many cases. Twenty-five new phylotypes were identified. Most teeth harbored a mixed consortium, with a mean number of 10 taxa per case. Only 11 taxa were found in more than one case, revealing a high interindividual variability in the composition of the microbiota.
Conclusion:  The current findings revealed new candidate endodontic pathogens, including as-yet-uncultivated bacteria and taxa other than E. faecalis , which may participate in the mixed infections associated with post-treatment apical periodontitis.