Paper of the week: Propidium monoazide-polymerase chain reaction for detection of residual periprosthetic joint infection in two-stage revision. Askar M, Sajid M, Nassif Y, Ashraf W, Scammell B, Bayston R. Mol Biol Rep. 2019 Oct 5. doi: 10.1007/s11033-019-05092-z.
Summary by Dr Sreeram Penna
In this study, researchers compare the efficacy of propidium monoazide-polymerase chain reaction (PMA-PCR or Viability PCR) for detecting residual periprosthetic joint infection in two-stage revision to a traditional polymerase chain reaction (PCR) and cultures. According to the authors, pre-treatment of propidium monoazide improves efficacy PCR testing by binding to residual DNA and RNA from the sample. Also, propidium monoazide does not cross the bacterial cell membrane and therefore, does not affect DNA from viable bacteria. Based on these actions authors postulate that by inhibiting residual DNA from both dead bacteria and human DNA in a sample using propidium monoazide, the overall efficacy of PCR in diagnosing infection is increased.
Cohort consists of 60 episodes of care in 58 patients. 14 of these episodes were considered infected using Muskulo Skeletal Infection Society criteria. The PCR assay done included only genus-specific primers for staphylococci and enterococci and species-specific primers for Cutibacterium acnes. Results showed that sensitivity of culture, PCR, and PMA-PCR were 50%, 71%, and 79%, respectively, and specificities were 98%, 72%, and 89%, respectively. Authors note that the increase in sensitivity of PMA-PCR compared to traditional PCR is due to the removal of large quantities of residual free-floating human DNA present in the sample by PMA.
In conclusion, PMA-PCR is better than traditional PCR with increased specificity and sensitivity. However, further research with broader PCR panel, including all possible bacteria causing PJI and larger sample size is needed.