Persistence of dead-cell bacterial DNA in ex vivo root canals and influence of nucleases on DNA decay in vitro

OBJECTIVE: The fate of DNA from bacteria that do not survive in the root canal is uncertain, yet DNA longevity may confound recovery of authentic etiologic participants in the disease process. This study assessed the recovery of PCR-detectable DNA in ex vivo human root canals and some environmental factors on the decay of microbial DNA. STUDY DESIGN: Heat-killed Enterococcus faecalis cells were inoculated into instrumented human root canals ex vivo, and samples were taken at intervals over 2 years and analyzed by polymerase chain reaction. In an in vitro assay, heat-killed E. faecalis cells and extracted E. faecalis DNA were inoculated into various media, DNase, and culture of a DNase-producing species, Prevotella intermedia. Recovery of DNA was assessed by gel electrophoresis. RESULTS: In ex vivo human teeth, amplifiable DNA was recovered after 1 and 2 years (in 14/15 and 21/25 teeth, respectively). In vitro experiments showed that extracted DNA incubated in different media (water, 10 -50 sera, and DNase) progressively decomposed to levels below the detection limit. In corresponding assays, cell-bound DNA was more resistant to decay. CONCLUSION: Amplifiable DNA is preserved after cell death, but the critical determinant is the form of DNA. Free DNA undergoes spontaneous and enzymatic decomposition, whereas cell-bound E. faecalis DNA persists for long periods.