Mycobacterium tuberculosis complex

Mycobacterium tuberculosis complex

Mycobacterium tuberculosis complex illustration

The Mycobacterium tuberculosis complex (MTBC) is a group of closely related mycobacteria that cause tuberculosis (TB) in humans and other animals. This complex includes several species, with Mycobacterium tuberculosis being the most prominent pathogen responsible for the majority of TB cases in humans.

Species within the Complex

The Mycobacterium tuberculosis complex consists of several species, each with varying host ranges and pathogenicity:

• Mycobacterium tuberculosis: The primary cause of tuberculosis in humans.
• Mycobacterium bovis: Primarily affects cattle but can also infect humans, often through the consumption of unpasteurized milk.
• Mycobacterium africanum: Found mainly in West Africa, it causes TB in humans and is less virulent than M. tuberculosis.
• Mycobacterium microti: Primarily infects small mammals but can occasionally cause disease in humans.
• Mycobacterium canettii: Rarely isolated, it is considered a progenitor of the MTBC.

Pathogenesis

The MTBC bacteria are aerobic and non-motile, with a characteristic waxy cell wall that makes them resistant to many common disinfectants and antibiotics. The bacteria are transmitted via aerosol droplets when an infected individual coughs or sneezes. Once inhaled, the bacteria can reach the alveoli of the lungs, where they are phagocytosed by macrophages.

Inside the macrophages, the bacteria can survive and multiply, leading to the formation of granulomas, which are the hallmark of TB infection. The immune response to the infection can lead to tissue damage and the characteristic symptoms of TB, such as cough, fever, night sweats, and weight loss.

Diagnosis

Diagnosis of TB caused by the MTBC involves a combination of clinical evaluation, tuberculin skin test (TST), interferon-gamma release assays (IGRAs), and microbiological culture of the bacteria. Chest X-rays are also used to identify lung involvement.

Treatment

Treatment of TB involves a prolonged course of multiple antibiotics to ensure the complete eradication of the bacteria and to prevent the development of antibiotic resistance. The standard treatment regimen includes isoniazid, rifampicin, ethambutol, and pyrazinamide.

Prevention

Prevention of TB includes vaccination with the BCG vaccine, which provides some protection against severe forms of TB in children. Public health measures to reduce transmission include contact tracing, isolation of infectious cases, and improving ventilation in crowded settings.

Related pages

• Tuberculosis
• Mycobacterium
• Antibiotic resistance
• Vaccination