Virulence Factors and Pathogenicity of Mycobacterium

Virulence, is referred as the ability of a pathogen to cause disease, and for mycobacteria it depends on their ability to reside within host cells and evade the microbicidal mechanisms of macrophages. The outcome of tuberculosis (TB) infection is highly variable and it seems that the closest relationship between the Mycobacterium genre and humans has shaped the mycobacterial genome to encode bacterial factors that reflects a highly evolved and coordinated program of immune evasion strategies that interfere with both innate and adaptive immunity causing disease even in fully immunocompetent host. Although Mycobacterium tuberculosis (MTB) does not have classical virulence factors, it has described many virulence-associated genes and virulence lifestyle genes from Mycobacterium tuberculosis complex (MTBC). In this chapter, we describe the most important gene/molecule involved in the host defense modulation response, also the plethora of strategies to evade immune mechanisms of macrophage. We review the main genes whose inactivation in the mycobacterial genome leads to a measurable loss in virulence in the different validated TB models.