Quantification and characterization of Synergistes in endodontic infections

Introduction: Bacterial species belonging to the poorly characterized division Synergistes have recently been reported in endodontic infections, and therefore may be part of the etiology of periradicular diseases. The objective of this study was to characterize and quantify the predominant Synergistes phylotypes in infected root canals. Methods: We analyzed 32 necrotic teeth, each from a different patient, with radiographic evidence of apical periodontitis and with primary endodontic infections. Results: Using real-time quantitative polymerase chain reaction based on Synergistes-specific primers, seven of the 32 cases were found to be positive. Comparative sequence analysis showed that each of the seven samples was infected by one numerically dominant phylotype. Diversity among phylotypes was such that they could be grouped into three major evolutionary branches within the Synergistes division. The size of the total Synergistes population ranged from 4.5 x 10(4) to 1.5 x 10(6) 16S rRNA gene copies, and the median proportion accounted for 0.79% of the total bacterial community. For comparison, we also quantified such recognized endodontic pathogens as Prevotella intermedia, Porphyromonas gingivalis, and Treponema. The first two species were found in five and nine cases, respectively, with a median proportion below 0.01%, while Treponema was found in 18 cases with a median proportion of 1.48%. Conclusion: Thus, the prevalence and quantity of Synergistes was clearly within the range of the other analyzed pathogens, suggesting their clinical relevance in endodontic infections. Furthermore, the diversity of Synergistes found at the diseased sites designates infected root canals as an important human ecosystem providing several unique micro-niches for this novel group of bacteria.