Detection and partial characterization of extracellular inducers of persistence in and .

This study describes the identification and partial characterization of persistence-inducing factors (PIFs) from staphylococci. Increases in persisters during mid-log phase growth indicate that quorum-sensing factors might be produced by staphylococci. To identify and partially characterize PIFs from RP62A and SH1000. Others have demonstrated a significant increase in persister numbers during mid-log phase. Inducers of this mid-log increase have yet to be identified in staphylococci. Optical density at 600 nm (OD) was used instead of time to determine when persister numbers increased during logarithmic growth. Concentrated culture filtrates (CCFs) from and were obtained at various ODs and following incubation at 16 h. The CCFs were used to develop a PIF assay. The PIF assay was used to partially characterize PIF from and for sizing of PIF activity, temperature and protease sensitivity and inter-species communications. The optimal ODs for and PIF assays were 2.0 and 0.5, respectively. The highest PIF activity for both species was from CCF following incubation overnight (16 h). ' PIF activity was decreased by storage at 4 C but not at 20 C (16 h), 37 C (1 h) or 100 C (15 min). ' PIF activity was decreased following storage at 4 C (2 weeks) and after boiling at 100 C for 5 min but not after incubation at 37 C (1 h). PIF activity from both species went through a 3000 molecular weight cutoff ultrafilter. Proteinase K treatment of PIF decreased activity but did not decrease the PIF activity of . PIF from did not increase persisters when used to treat cells and nor did PIF from increase persisters when used to treat cells. Attempts to discover PIFs for staphylococci were unsuccessful due to the time-based means used to identify mid-log. Both staphylococcal species produce extracellular, low-molecular-weight inducers of persistence when assayed using an OD -based PIF assay.