Insights in to Chronicity of P. gingivalis: Viable but Non-culturable State (VBNC)

Objectives: Bacterial species have evolved multiple mechanisms to survive ecological, nutritional and chemical stresses as well as host cell defenses. Among these is to enter a viable but non-culturable (VBNC) state. The ability of a bacterial species to enter the VBNC state and also resuscitate from this state is now recognized as an important mechanism for the survival and pathogenesis of several bacterial pathogens, especially those that are associated with chronic infections. Oral bacteria such as P. gingivalis (Pg) are etiological agents of a variety of extra oral infections, especially those of the cardiovascular system and are implicated in the initiation and/or progression of atherosclerotic cardiovascular disease. In this study we sought to determine the ability of Pg to shift from a culturable to the VBNC state under conditions of cellular physiological stress.
Methods: P.gingivalis W83 was grown in TSB media under acidic and oxidative stress conditions to determine the ability to enter a VBNC state and to evaluate physiological changes during their shift from the culturable to VBNC. We also evaluated the ability of P.gingivalis to shift to VBNC intracellularly in human coronary artery Endothelial Cells (HCAECs).
Results: There was a dramatic shift from the culturable to VBNC state when PgW83 was grown under acidic conditions or exposed to oxidative stress after 48-72 hours of culture in TSB media. Furthermore, we observed a decrease in culturable PgW83 isolated from human coronary artery endothelial cells (HCAECs) at 48-72 hour post-infection. Live/Dead staining demonstrated that intracellular PgW83 were viable even at 72hrs of infection; despite the lack of recoverable CFUs, indicating that these bacteria were in a VBNC state..
Conclusions: This study is the first to determine the adaptation of changes in lifestyle of P.gingivalis and provides directions to better define P.gingivalis pathogenicity and chronicity.