Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) is a pathogenic bacterial species in the family Mycobacteriaceae and the causative agent of tuberculosis (TB), one of the most significant infectious diseases worldwide.

TB Culture

Overview

M. tuberculosis was first identified as the cause of tuberculosis by Robert Koch in 1882. It is an obligate aerobe that is acid-fast, non-motile, and non-spore-forming. The bacterium has an unusually waxy cell wall that is rich in mycolic acids, giving it unique properties and making it difficult to stain with traditional Gram stain.

Pathogenesis and Transmission

M. tuberculosis is spread primarily by airborne droplets when individuals with active pulmonary tuberculosis cough, sneeze, or speak. Upon inhalation, the bacteria are phagocytosed by alveolar macrophages in the lungs. However, the bacterium has developed mechanisms to evade the immune response, enabling it to survive and replicate within the macrophages. This process leads to the formation of granulomas, a characteristic feature of tuberculosis.

Disease Manifestation

The primary site of M. tuberculosis infection is the lungs, leading to pulmonary tuberculosis. Symptoms can include a chronic cough with blood-containing sputum, fever, night sweats, and weight loss. However, the bacterium can disseminate to other organs through the bloodstream, causing extrapulmonary tuberculosis. This can affect any organ but most commonly involves the lymph nodes, pleura, genitourinary tract, bones and joints, and the central nervous system.

Diagnosis and Treatment

• The diagnosis of tuberculosis can be challenging due to the slow growth rate of M. tuberculosis and non-specific symptoms. It primarily relies on sputum microscopy, sputum culture, and molecular techniques like the nucleic acid amplification tests. The tuberculin skin test (TST) and Interferon-gamma release assays (IGRAs) are used to identify latent tuberculosis infection.
• Treatment generally involves a six-month regimen of multiple antibiotics, including isoniazid, rifampicin, pyrazinamide, and ethambutol.

Prevention

The Bacillus Calmette–Guérin (BCG) vaccine offers some protection against tuberculosis, especially in children. In adults, its protective effect is variable. Other preventive strategies include early detection and treatment of active cases to reduce transmission.