Detection of Bacteroides forsythus and Porphyromonas gingivalis in infected root canals during periapical periodontitis by 16S rDNA

Periapical periodontitis is termed when inflammation of the periodontium is caused by irritants of endodontic origin. Bacterial strains in the root canals were not easy to be identified by the traditional agar culture. In this study a 16S rDNA-based polymerase chain reaction detection method was used to determine the occurrence of Bacteroides forsythus and Porphyromonas gingivalis in chronic periapical periodontitis among Chinese patients. 217 patients with chronic periapcial periodontitis were recruited and a total of 266 teeth were collected. The subjects had no systemic diseases, no antibiotics taken, no root canal treatment (RCT) performed on the infected teeth in the last 3 months. The DNA of bacteria in the root canal was extracted and amplified using universal 16S rDNA primers. The amplification was performed to detect B. forsythus and P. gingivalis using oligonucleotide primers designed from species-specific 16S rDNA signature sequences. B. forsythus and P. gingivalis were detected in 26 and 40% of the participants, respectively. 24 out of 217 infected root canals demonstrated the existence of both types of bacteria, the utility of a 16S rDNA-based PCR detection method showed high sensitivity and high specificity to directly detect B. forsythus, P. gingivalis or other pulpal microorganisms from samples of root canal infections. The results indicated that B. forsythus or P. gingivalis might be a member of the microbiota associated with chronic periapical periodontitis and there was a strong association between the studied species and periodontitis.