[Virulence factors of Mycobacterium tuberculosis]

Mycobacterium tuberculosis, the etiological agent of human tuberculosis, causes annually three million deaths and latently infects about two billion people. Immunodeficiency caused by malnutrition, senescence or co-infection with HIV enhances the risk of developing active tuberculosis, either from a primary infection or by reactivation of a latent infection. The increasing appearance of multidrug-resistant strains to existing drugs is worrisome, since it leaves patients practically without treatment options. The understanding of the mechanisms of transmission, pathogenesis and virulence of M. tuberculosis is important. The analysis of its genome shows the presence of alternative sigma factors, transcriptional repressors and activators, two component signaling systems, metabolic enzymes and cellular secretory systems, that are associated with virulence in a series of pathogenic micro-organisms. Environmental stimuli such as pH, temperature, osmolality, oxygen availability are processed, activating or repressing virulence genes. The molecular mechanisms of action of these genes have been elucidated in in vitro and in vivo models.