Mycobacterium

Mycobacterium is a genus of aerobic, non-motile bacteria in the family Mycobacteriaceae. They are Gram-positive in appearance but are best characterized by acid-fast staining due to a waxy, lipid-rich cell wall containing mycolic acids. This lipid envelope makes them resistant to many dyes, desiccation, and some antibiotics. Many species are slow-growing, with colonies taking days to weeks to appear.

Key human pathogens include the Mycobacterium tuberculosis complex and M. leprae, which cause tuberculosis and leprosy, respectively. Other species, such as M. avium complex (MAC), M. kansasii, and M. marinum, are environmental and opportunistic pathogens. Transmission varies by species: M. tuberculosis is primarily airborne; M. bovis is zoonotic; NTMs are often acquired from water and soil.

Pathogenesis and features: Many species survive within macrophages, forming granulomas in susceptible hosts. The mycobacterial cell wall contributes to persistence and intrinsic resistance to some antibiotics and disinfectants. Diagnosis relies on acid-fast staining and culture on selective media like Löwenstein-Jensen, along with molecular assays. Cultivation is slow, and some species, including M. leprae, cannot be grown in standard artificial media.

Treatment and prevention: Infections require prolonged multidrug regimens tailored to species and drug susceptibility. Tuberculosis regimens often include isoniazid, rifampicin, pyrazinamide, and ethambutol, with adjustments for resistance. MDR-TB and XDR-TB are major public health concerns. The BCG vaccine provides variable protection against severe pediatric TB and is used in some regions.

History and context: The role of Mycobacterium in tuberculosis was established in the late 19th century, notably with Robert Koch’s identification of the causative agent in 1882. The genus encompasses both pathogenic species and environmental organisms with diverse clinical and ecological roles.

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