Controlled cellular redox, repressive hemin utilization and adaptive stress responses are crucial to metronidazole tolerance of Porphyromonas gingivalis persisters.

BACKGROUND: Antimicrobial-tolerant microbial persisters critically account for various infections and inflammation. This study identified the characteristics of Porphyromonas gingivalis persisters, and explored their underlying survival mechanisms through proteomic profiling.

METHODS: Porphyromonas gingivalis cultured with different concentrations of hemin was treated with 100 μg/ml of metronidazole (MTZ). The viability of P. gingivalis persisters was determined by colony-forming unit assay and LIVE/DEAD staining. The proteomic signature of P. gingivalis persister fractions was examined using LC-MS/MS and bioinformatic analysis.

RESULTS: A small fraction of P. gingivalis persisters survived from lethal MTZ treatment without heritability. At late exponential phase, the frequency of these persisters significantly increased when incubated with 1 μg/ml of hemin compared to 10 μg/ml. Higher levels of P. gingivalis persisters formed at stationary phase than the late exponential phase. High-throughput proteomic analysis showed that the persisters markedly downregulated multiple proteins involved in electron transfer and heme/iron utilization essential for redox regulation and MTZ activation. Moreover, the persisters enabled to shut down major cellular activities (e.g. translation) and overexpress stress proteins.

CONCLUSION: The presence and survival of metronidazole-tolerant P. gingivalis persisters may be dominated by regulation of cellular redox state and enhanced via repression of heme/iron utilization, dormancy and stress responses.