Bacterial DNA persists for extended periods after cell death

The fate of DNA from bacteria that infect the root canal but cannot survive is currently unknown, yet such information is essential in establishing the validity of polymerase chain reaction (PCR)-based identification methods for root canal samples. This in vitro study tested the hypothesis that PCR-detectable DNA from dead bacteria might persist after cell death and investigated the efficiency of sodium hypochlorite (NaOCl) as a field decontamination agent. Using heat-killed Enterococcus faecalis, the persistence of DNA encoding the 16S rRNA gene was monitored by PCR. While most probable number analysis showed an approximate 1000-fold decay in amplifiable template, E. faecalis DNA was still PCR-detectable 1 year after cell death. NaOCl (1%) eliminated amplifiable DNA within 60 seconds of exposure. Our findings also disclosed a previously overlooked problem of concentration-dependent inhibition of the PCR reaction by thiosulfate-inactivated NaOCl. These results highlight the challenges of reliably identifying the authentic living root canal flora with PCR techniques.