CONICET | Buscador de Institutos y Recursos Humanos

Mycobacterium tuberculosis (Mtb) is a highly successful pathogen with substantial intra-species variability. We have previously demonstrated that Mtb replication within macrophages does not necessarily correlate to epidemiologicalsuccess, as the multidrug resistant outbreak Mtb strain M is less able to replicate within human monocyte-derived macrophages (MDM) than its sporadic variant strain 410. IFNgamma is a key cytokine for a protective response in tuberculosis, and differences in IFNgamma-induced macrophage activation can unveil differences between infecting strains. We hypothesized that M-variant 410 is more susceptible to IFNgamma challenge than the prototype M strain. Methods: Two prototype M strain representatives (Mtb 6548 and 15526), M-variant 410 and reference strain H37Rv were grown in 7H9-AD-0.05% Tween. Cultures at late log phase were used to infect 7-day MDM at a multiplicity of infection of 1. After 1 hour, MDM from 6 healthy donors were stimulated or not with 100U/ml IFNgamma. CFU/ml were counted by plating serial dilutions of the lisates at 24 hours of infection. Results: In line with previous reports, IFNgamma was unable to consistently enhace micobactericidal activity of MDM. Although a trend towards enhanced control was observed for strain 410, values did not achieve statistical significance against the other strains. Paradoxically, greater CFU/ml were recovered for some donors/strains, particularly for H37Rv. Conclusions: These preliminary results do not support the idea of strain 410 having an impaired ability to evade IFNgamma-activated effector mechanisms. Experiments are ongoing aimed to enhance sample size and to evaluate the influence of MDM viability on the outcome.