Mycobacteria A15 - A19

Species of the genus Mycobacterium are aerobic, non-spore-forming, alcohol- and acid-fast, Gram-positive, slender, immotile rods with a worldwide distribution. The genus Mycobacterium includes approximately 170 species. Common characteristic of these bacteria is the so-called acid fastness in the Ziehl-Neelsen stain. M. tuberculosis is the most important mycobacterium worldwide as a causative agent of tuberculosis. The Mycobacterium tuberculosis complex includes various pathogens of skin infections such as M. tuberculosis, M. africanum, M. bovis and others.

Leprosy is an independent infectious complex which is very rare in Germany.

All other septa of the genus Mycobacterium are called "non-tuberculous mycobacteria" (NTM) or "mycobacteria other than tuberculosis" (MOTT). NTMs occur in the environment (soil, water). Isolation of "non-tuberculous mycobacteria" from patient material cannot necessarily be assumed to be a real "disease".

The most important pathogenic mycobacteria include:

Mycobacterium tuberculosis - complex (considered to be the causative agent of human tuberculosis)

• Mycobacterium tuberculosis var. hominis and bovis
• Mycobacterium africanum (tuberculosis mainly in Africa)
• Mycobacterium caprae (transmitted to humans from cattle and other animals)öwen
• Mycobacteriumbovis (transmitted from cattle and other animals to humans)
• Mycobacterium microti (tuberculosis of the vole, can be transmitted to humans from here)
• Mycobacterium canetti (still found in Africa)
• Mycobacterium pinipedii (has animals as reservoir, e.g. sea lions)
• Mycobacterium leprae

Non-tuberculous mycobacteria (NTM)

• Mycobacterium fortuitum complex (MFK)
• Mycobacteriumavium complex (pulmonary and extrapulmonary infections)
• Mycobacterium scrofulaceum (lymphadenitis)
• Mycobacteriumkansasii (pulmonary infections)

• Mycobacterium marinum (see below swimming pool granuloma)

Rare mycobacteria:

• Mycobacterium chelonei
• Mycobacterium flavescens
• Mycobacterium gordonae
• Mycobacterium smegmatis
• Mycobacterium terrae
• Mycobacterium vaccae (different clinical pictures, each described only in individual cases)

Mycobacteria are "acid-proof". Free mycol acids in the cell wall form a complex bond with carbolic fuchsine (fuchsin + phenol). This staining is not decolorized by HCl alcohol. The "non-acid-resistant" bacteria, however, are decoloured (principle of Ziehl-Neelsen staining). The decoloured, non-acid-resistant bacteria can be counterstained, for example, with malachite green. The acid-resistant bacteria do not stain.

Tuberculosis is still widespread throughout the world. About 1/3 of the world's population is infected, of which about one in 10 will experience active tuberculosis in the course of their lives.

Culture: The cell division of the tuberculosis bacteria is slow and occurs at intervals of 18 - 20 hours. Cultures will therefore be observed over a period of several weeks. Colonies can be detected after 3 - 4 weeks at the earliest. The resistance of tuberculosis bacteria to tuberculostatics can be determined in about one week. The growth of mycobacteria is tested in the presence of different tuberculostatics.

Animal experiment: Is dispensable in routine diagnostics.

Molecular biological detection: Possible for M. tuberculosis complex, M. kansasii and M. avium intracellular complex. The pathogens can be identified by their nucleic acid sequence. For this purpose they must be cultured beforehand. The corresponding nucleic acid sections are amplified with a polymerase chain reaction (PCR). Note: Nucleic acid sequencing also allows the identification of exotic mycobacteria that cannot be cultivated in the laboratory.

Resistance testing: Pulmonary tuberculosis must be treated for 6 months. The most common drugs are isoniazid (INH), rifampicin (RMP), pyrazinamide (PZA), ethambutol (EMB) and streptomycin (SM). Resistance must be taken into account, especially in the case of non-tuberculous mycobacteria. Resistance exists if the pathogens grow on a culture medium despite the addition of tuberculostatics.