Virulence hierarchies within the Mycobacterium tuberculosis complex.

Area of Science:

• Microbiology
• Immunology
• Veterinary Medicine

Background:

• The Mycobacterium tuberculosis complex (MTBC) comprises M. tuberculosis (M. tb), M. bovis, and M. orygis, all significant threats to human and animal health.
• Understanding pathogenicity differences among these closely related MTBC members is crucial for disease control.

Purpose of the Study:

• To comparatively assess the virulence of M. tb, M. bovis, and M. orygis.
• To identify key factors contributing to differential pathogenicity within the MTBC.

Main Methods:

• Comparative virulence assessment in bovine (Holstein calves) and murine (C57BL/6 mice) infection models via aerosol inoculation.
• Pathological analysis (macroscopic, microscopic, bacterial burden) and survival studies.
• Gene disruption and proteomic analyses to identify virulence factors.

Main Results:

• Animal-adapted MTBCs (M. bovis, M. orygis) exhibited significantly enhanced virulence compared to M. tb in both models.
• Distinct immunopathology and rapid mortality (within 24 days) were observed in mice infected with M. bovis or M. orygis.
• Virulence was dependent on shared (ESAT-6) and lineage-associated (MPT70) factors, route of infection, and host immune status.

Conclusions:

• Unexpected virulence hierarchies exist within the MTBC, with animal-adapted strains being more virulent.
• Findings have fundamental and translational implications for tuberculosis research and control strategies.
• Specific virulence factors and host-pathogen interactions dictate MTBC pathogenicity.