This study performed barcoded multiplex pyrosequencing with a 454 FLX instrument to compare the microbiota of dental\nroot canal infections associated with acute (symptomatic) or chronic (asymptomatic) apical periodontitis. Analysis of\nsamples from 9 acute abscesses and 8 chronic infections yielded partial 16S rRNA gene sequences that were taxonomically\nclassified into 916 bacterial species-level operational taxonomic units (OTUs) (at 3% divergence) belonging to 67 genera and\n13 phyla. The most abundant phyla in acute infections were Firmicutes (52%), Fusobacteria (17%) and Bacteroidetes (13%),\nwhile in chronic infections the dominant were Firmicutes (59%), Bacteroidetes (14%) and Actinobacteria (10%). Members of\nFusobacteria were much more prevalent in acute (89%) than in chronic cases (50%). The most abundant/prevalent genera in\nacute infections were Fusobacterium and Parvimonas. Twenty genera were exclusively detected in acute infections and 18 in\nchronic infections. Only 18% (n = 165) of the OTUs at 3% divergence were shared by acute and chronic infections. Diversity\nand richness estimators revealed that acute infections were significantly more diverse than chronic infections. Although a\nhigh interindividual variation in bacterial communities was observed, many samples tended to group together according to\nthe type of infection (acute or chronic). This study is one of the most comprehensive in-deep comparisons of the microbiota\nassociated with acute and chronic dental root canal infections and highlights the role of diverse polymicrobial communities\nas the unit of pathogenicity in acute infections. The overall diversity of endodontic infections as revealed by the\npyrosequencing technique was much higher than previously reported for endodontic infections.
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