mycobacterias

Mycobacteria are a diverse group of aerobic, nonmotile bacteria belonging to the phylum Actinobacteria. They are characterized by a thick, waxy cell wall rich in mycolic acids, which gives them distinctive acid-fast staining properties and resistance to many common disinfectants. They are commonly found in soil and water and can persist in the environment. Growth in culture is generally slow, with many species taking weeks to form visible colonies; a subset known as rapid growers can appear within days to a couple of weeks.

Taxonomy and appearance: The genus Mycobacterium comprises many of the clinically important species, though related genera within the Mycobacteriaceae are also recognized. The organisms are rods (bacilli) that tend to form variable pigment and waxy colonies. Growth rates vary widely: most pathogenic mycobacteria are slow-growing, while rapid growers such as M. fortuitum, M. chelonae, and M. smegmatis are exceptions.

Pathogenicity and diseases: The most prominent human pathogens are Mycobacterium tuberculosis and Mycobacterium leprae, which cause tuberculosis and leprosy, respectively. A large group of non-tuberculous mycobacteria (NTM), including M. avium complex, M. kansasii, M. abscessus, and M. fortuitum, can cause pulmonary disease, lymphadenitis, skin and soft tissue infections, or disseminated disease, particularly in immunocompromised individuals. Transmission differs by organism: TB is spread through person-to-person aerosols; leprosy is less contagious and involves delayed nerve and tissue damage; NTMs are typically acquired from the environment rather than contracted from other people.

Diagnosis and treatment: Diagnosis relies on acid-fast staining, culture on specialized media (Löwenstein-Jensen or Middlebrook) or liquid systems, and nucleic acid amplification tests. Treatment requires species- and site-specific regimens, with long durations and careful antibiotic stewardship. TB usually involves multi-drug therapy over six months or longer, while leprosy uses multi-drug regimens for several months to years. NTM infections are treated with tailored combinations, often including macrolides, and regimens vary by species and infection site. Vaccination with BCG is used in some countries to reduce severe TB in children, though its effectiveness against adult pulmonary TB is variable.

Public health and research: Control emphasizes early diagnosis, appropriate therapy, infection control, and vaccination where applicable. Research areas include improved diagnostics, vaccines, new antimicrobials, and genomic studies to refine taxonomy, pathogenesis, and treatment strategies.