Root canal microbiota of teeth with chronic apical

21 Samples from infected root canals of 43 teeth with chronic apical periodontitis 22 were analyzed for the presence and relative levels of 83 oral bacterial 23 species/phylotypes using a reverse-capture checkerboard hybridization assay. 24 Associations between the most frequently detected taxa were also recorded. The 25 most prevalent taxa were Olsenella uli (74%), Eikenella corrodens (63%), 26 Porphyromonas endodontalis (56%), Peptostreptococcus anaerobius (54%), and 27 Bacteroidetes oral clone X083 (51%). When prevalence was considered only for 28 bacteria present at levels >10, Bacteroidetes clone X083 was the most frequent 29 (37%), followed by Parvimonas micra (28%), E. corrodens (23%), and Tannerella 30 forsythia (19%). The number of target taxa per canal was directly proportional to 31 the size of apical periodontitis lesion, with lesions >10 mm in diameter harboring a 32 mean number of approximately 20 taxa. Several positive associations were for the 33 first time disclosed for the most prevalent taxa, and may have important ecological 34 and pathogenic implications. In addition to strengthening the association of 35 several cultivable named species with chronic apical periodontitis, the present 36 findings using a large-scale analysis allowed inclusion of some newly named 37 species and as-yet-uncultivated phylotypes in the set of candidate pathogens 38 associated with this disease. 39