SUSCEPTIBILITY OF A PANEL OF VIRULENT-STRAINS OF MYCOBACTERIUM-TUBERCULOSIS TO REACTIVE NITROGEN INTERMEDIATES

Murine bone marrow-derived macrophages were infected with a panel of v irulent isolates of Mycobacterium tuberculosis including laboratory st rains Erdman and H37Rv and various clinical isolates in order to deter mine the sensitivity of each of these strains to the antimycobacterial activities of macrophage-generated reactive nitrogen intermediates (R NI). All of the M. tuberculosis strains grew in murine bone marrow der ived macrophages; however, gamma interferon-primed macrophages limited the initial growth of intracellular bacilli. Some of the mycobacteria l strains, including Erdman, were killed over the first 4 days of infe ction, as evidenced by significant decreases in the number of viable i ntracellular bacilli determined by a CFU assay. Other mycobacterial st rains were not killed during this same period, and some isolates, incl uding CSU 24 and CSU 31, grew steadily in activated macrophages. The a ccumulation of nitrite on infected monolayers was measured, and it was found that inhibitory levels of RNI did not vary among infections wit h the different strains. Nitrite tolerance was determined in a cell-fr ee system fbr each of the strains in order to compare susceptibilities of the strains to RNI. All of the strains tested were killed by level s of RNI generated by the acidification of 10 mM NaNO2 to pH 6.5 or 5. 5, and the strains exhibited a range of tolerance to lower concentrati ons of RNI. No correlations were observed between such cell-free RNI t olerances and the capacity of bacilli to resist macrophage RNI-mediate d killing. These results indicate that under stringent conditions, RNI can kill M. tuberculosis, but that under less harsh, more physiologic al conditions, the effects of RNI range from partial to negligible inh ibition.