Survival of an epidemic MDR strain of Mycobacterium tuberculosis and its non-prosperous variant within activated macrophages.

The fitness of a pathogen results from the interaction of multiple factors favoring either epidemiological success or failure. Herein, we studied the performance of the M strain, a highly successful multidrug resistant Mycobacterium tuberculosis genotype, and its non-prosperous variant, the 410 strain, in activated human monocyte-derived macrophages. Both strains showed comparable ability to induce necrotic cell death and to survive in apoptotic macrophages. Of the various macrophage activation conditions tested, none led to an enhanced control of the outbreak strain. The combination of 1,25(OH) vitaminD3 and IFN-γ favored significantly the control of the non-prosperous 410 strain. These observations indicate that the ability of the M strain to survive within the hostile intracellular milieu is conserved, and the overall fitness cost paid by this genotype would be low. Our results provide additional evidence on bacterial traits that may have contributed to the epidemiological success of the M strain.