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DOI: 10.1101/2021.11.22.468319

Bovine serum albumin promotes reactivation of viable but non-culturable Mycobacterium tuberculosis via activation of protein kinase-dependent cell division processes

Y.Morishige Y. Murase K. Chikamatsu ...+7 S. Mitarai
Objective: Mycobacterium tuberculosis (Mtb) H37Ra strain has been reported to rapidly enter the viable but non-culturable (VBNC) state following treatment with an NADH oxidase inhibitor (diphenyleneiodonium [DPI]) and to be reactivated by fetal bovine serum (FBS). However, the mechanism underlying FBS-induced reactivation is unclear. We tried to reveal the mechanism of FBS-induced reactivation using M. tuberculosis H37Rv. Methods: First, we evaluated the effect of DPI on culturability, viability and changes of acid-fastness toward H37Rv. Secondly, we measured the reactivation-promoting effects of human serum albumin, egg-white albumin and antioxidative agents in DPI-induced VBNC cells. We also inhibited adenylyl cyclase and protein kinase which is the downstream of adenylyl cyclase to evaluate the influence to reactivation capacity of bovine serum albumin (BSA). Results: DPI treatment induced VBNC state in H37Rv, resulting in a high proportion of viable cells but a low proportion of culturable cells, loss of acid-fastness and lipid-accumulation. Not only FBS but also BSA alone could reactivate H37Rv. Contrary to our expectation, only human serum albumin had a similar restorative effect to BSA. The inhibition of adenylyl cyclase by SQ22536 did not have a significant effect on reactivation; however, the inhibition of mycobacterial protein kinase by H89 and staurosporine strongly suppressed the BSA-induced reactivation. Conclusion: DPI-induced VBNC Mtb cells may be reactivated via the activation of protein kinase-dependent cell division processes through interaction with BSA.