Low concentrations of nitric oxide exert a hormetic effect on Mycobacterium tuberculosis in vitro

Abstract

Susceptibilities of 12 clinical Mycobacterium tuberculosis isolates to acidified sodium nitrite (ASN) were compared. The results demonstrate that 8 of the 12 isolates exhibited enhanced survival levels in 1.5 mM ASN compared to levels in medium alone, suggesting that low concentrations of reactive nitrogen intermediates have a hormetic effect on M. tuberculosis in vitro.

FIG. 1.

Mycobacterial ASN susceptibility assays. Mycobacterial isolates were incubated for 16 h in 7H9 medium (pH 5.4) and then plated onto 7H11 agar. CFU were determined at 28 days of incubation. Results for unexposed isolates incubated in 7H9 medium (pH 5.4) without NaNO₂ and isolates exposed to 1.5 mM NaNO₂ and 6 mM NaNO₂ (as identified to right of figure) are demonstrated as percent survival based on the CFU recovered from ASN-exposed strains relative to the CFU recovered from unexposed strains. The data are representative of triplicate experiments showing mean values of triplicate cultures for each strain. Bars represent standard errors. Mtb, M. tuberculosis; ID, identification.