Bacterial Cause of Tuberculosis
Tuberculosis (TB) is caused by bacteria of the Mycobacterium tuberculosis complex, most commonly Mycobacterium tuberculosis itself. 1
Primary Causative Organism
Mycobacterium tuberculosis (MTB) is the principal bacterial agent responsible for human tuberculosis, accounting for the vast majority of TB cases worldwide 1
The organism is classified as a gram-positive, acid-fast bacillus that forms progressive granulomatous infections 2
MTB is characterized by its thick, waxy cell wall, slow growth rate in culture, and intrinsic drug resistance mechanisms 3
Other Members of the Mycobacterium tuberculosis Complex
While M. tuberculosis is the predominant cause, other species within the complex can cause human disease:
Mycobacterium bovis can infect humans, typically through consumption of contaminated milk, milk products, or meat from infected animals 2
- In some developing countries, up to 10% of human tuberculosis cases are attributed to M. bovis 2
Mycobacterium africanum causes TB in humans but is much less common than M. tuberculosis 2
Mycobacterium microti is not known to cause TB in humans 2
Mycobacterium avium infection in humans is very rare 2
Key Pathogenic Characteristics
MTB is an expert pathogen with the ability to enter non-replicating states for prolonged periods, causing latent infection that can persist for years 3
The bacterium can replicate inside macrophages and expresses diverse immunomodulatory molecules that allow it to evade host immune responses 3
MTB demonstrates metabolic remodeling during chronic infection, contributing to its survival in hostile host environments 3
Clinical Significance
TB remains the ninth leading cause of death worldwide and the leading cause of mortality by a single infectious agent, with over 1.8 million deaths annually 4, 3
The disease primarily affects the lungs (pulmonary TB) but can also affect intestines, meninges, bones, joints, lymph nodes, skin, and other tissues (extrapulmonary TB) 2