Other meanings of Mycobacterium tuberculosis
Microbiology
Mycobacterium tuberculosis is a pathogenic bacterium and the primary causative agent of tuberculosis (TB), one of the deadliest infectious diseases in human history. It is an acid-fast, aerobic, non-motile, slow-growing bacillus with a unique lipid-rich cell wall that confers resistance to desiccation and many disinfectants. The World Health Organization estimates that approximately one-quarter of the global population is latently infected, with about 10.6 million new active TB cases and 1.3 million deaths in 2022 alone1.
M. tuberculosis is a member of the Mycobacterium tuberculosis complex (MTBC), which includes closely related species such as M. bovis and M. africanum. Its cell wall is exceptionally rich in mycolic acids, long-chain fatty acids that contribute to acid-fastness and impermeability, providing intrinsic resistance to many antibiotics and host immune defenses1. The bacterium is an obligate aerobe, grows slowly (generation time 15–20 hours), and forms rough, buff-colored colonies on solid media. Its genome, first sequenced for the reference strain H37Rv in 1998, is approximately 4.4 million base pairs with a high guanine-cytosine (GC) content of 65.6%2. Virulence factors include the ESX-1 secretion system, which exports proteins such as ESAT-6 and CFP-10, and the glycolipid trehalose dimycolate (cord factor), which disrupts host mitochondrial membranes and inhibits phagosome maturation.
Transmission occurs via airborne droplets; inhaled bacilli reach the alveoli and are phagocytosed by alveolar macrophages. M. tuberculosis evades killing by blocking phagosome-lysosome fusion, resisting reactive oxygen and nitrogen species, and modulating host cytokine responses3. Infected macrophages recruit immune cells, forming a granuloma—the hallmark of TB pathology. Within the granuloma, bacteria can enter a dormant state, enabling lifelong latent infection in about 90% of immunocompetent individuals. Reactivation, often triggered by immunosuppression (e.g., HIV co-infection, TNF-α inhibitors), leads to active disease, most commonly in the lungs (pulmonary TB) but also in extrapulmonary sites such as lymph nodes, pleura, and bone.
Diagnosis relies on smear microscopy, culture (the gold standard), molecular tests (e.g., GeneXpert MTB/RIF), and imaging. Standard treatment for drug-susceptible TB consists of a 2-month intensive phase with rifampin, isoniazid, pyrazinamide, and ethambutol, followed by a 4-month continuation phase with rifampin and isoniazid4. Multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) threaten global control; resistance arises primarily through chromosomal mutations in target genes such as rpoB (rifampin) and katG (isoniazid). Newer regimens (e.g., bedaquiline, pretomanid, linezolid) have improved outcomes for MDR-TB, but access remains limited5.
M. tuberculosis has no known environmental reservoir; humans are its only natural host. The reference strain H37Rv, isolated from a patient in 1905, remains the most widely studied strain and is avirulent in guinea pigs—a quirk that has puzzled researchers for decades2. Another notable fact is that the bacterium can survive in a non-replicating, drug-tolerant state in necrotic granuloma caseum, a phenomenon that underpins the need for prolonged therapy. The BCG vaccine, derived from M. bovis, provides variable protection, especially against miliary and meningeal TB in children, but its efficacy against pulmonary TB in adults is inconsistent6. Genetically, M. tuberculosis exhibits a clonal population structure with six major lineages associated with specific human migrations, and the Beijing lineage is linked to increased drug resistance and virulence1.
Tuberculosis remains a leading infectious cause of death worldwide, with the WHO End TB Strategy aiming for a 90% reduction in incidence by 2035. Research focuses on understanding the molecular basis of dormancy, developing a more effective vaccine, and shortening treatment duration. Notable advances include the identification of a novel lipid biosynthesis pathway (e.g., mycolic acid cyclopropanation) as a drug target, and the use of CRISPR interference to study essential genes7. The bacterium's ability to manipulate host immunity through secreted effectors continues to be a fertile area of investigation, with implications for both TB and autoimmunity.
This article focuses on the bacterium M. tuberculosis, not on the clinical disease tuberculosis itself.
Help improve the encyclopedia. Reports go straight to the site manager.