Molecular characterization of the microbial flora residing at the apical portion of infected root canals of human teeth

Introduction: This study investigated the bacterial communities residing in the apical portion of human teeth with apical periodontitis in primary and secondary infections by using a culture-independent molecular biology approach.

Methods: Root canal samples from the apical root segments of extracted teeth were collected from 18 teeth with necrotic pulp and 8 teeth with previous endodontic treatment. Samples were processed for amplification via polymerase chain reaction and separated with denaturing gradient gel electrophoresis. Selected bands were excised from the gel and sequenced for identification.

Results: Comparable to previous studies of entire root canals, the apical bacterial communities in primary infections were significantly more diverse than in secondary infections (P = .0003). Interpatient and intrapatient comparisons exhibited similar variations in profiles. Different roots of the same teeth with secondary infections displayed low similarity in bacterial composition, whereas an equivalent sample collected from primary infection contained almost identical populations. Sequencing revealed a high prevalence of Fusobacteria, Actinomyces species, and oral Anaeroglobus geminatus in both types of infection. Many secondary infections contained Burkholderiales or Pseudomonas species, both of which represent opportunistic environmental pathogens.

Conclusions: Certain microorganisms exhibit similar prevalence in primary and secondary infection, indicating that they are likely not eradicated during endodontic treatment. The presence of Burkholderiales and Pseudomonas species underscores the problem of environmental contamination. Treatment appears to affect the various root canals of multirooted teeth differently, resulting in local changes of the microbiota.