A genus of aerobic, nonmotile bacteria (family Mycobacteriaceae) containing Gram-positive, acid-fast, slender, straight or slightly curved rods; slender filaments occasionally occur, but branched forms rarely are produced. Parasitic and saprophytic species occur. A number of species are associated with infections in immunocompromised people, especially those with AIDS. The type species is M. tuberculosis. It is the type genus of the family Mycobacteriaceae. [myco- + bacterium]
- M. abscessus SYN: M. chelonae abscessus.
- M. avium a bacterial species causing tuberculosis in fowl and other birds. Causes opportunistic infections in humans.
- M. avium-intracellulare complex an opportunistic agent of infection, particularly in people with AIDS. Difficult to treat because M. avium-intracellulare is resistant to many antibiotics. The organism may also cause chronic lower respiratory tract infections in patients who are not severely immunocompromised, especially those with underlying abnormal lung parenchyma.
- M. bovis a bacterial species that is the primary cause of tuberculosis in cattle; transmissible to humans and other animals, causing tuberculosis. SYN: tubercle bacillus (2).
- M. chelonae rapid-growing m. (Runyon group IV) that cause sporadic infection in any tissue or organ system in humans following cardiothoracic surgery, peritoneal- and hemodialysis, augmentation mammaplasty, arthroplasty, and immunocompromised patients.
- M. chelonae abscessus a bacterial species originally found in a traumatic infection of the knee. SYN: M. abscessus.
- M. fortuitum a saprophytic bacterial species found in soil and in infections of humans, cattle, and cold-blooded animals. Causes skin abscesses.
- M. intracellulare a bacterial species found in lung lesions and sputum of humans; may cause bone and tendon-sheath lesions in rabbits; some strains are pathogenic for mice. Recently linked to opportunistic infections in humans. SYN: Battey bacillus.
- M. kansasii a bacterial species causing a tuberculosislike pulmonary disease; found to cause rare infections (and usually lesions) in spinal fluid, spleen, liver, pancreas, testes, hip joint, knee joint, finger, wrist, and lymph node s.
- M. leprae a bacterial species that causes Hansen disease (leprosy); an obligatory intracellular m. that has not been propagated in the laboratory, but that will survive in the 9-banded armadillo (Dasypus novemcinctus). SYN: Hansen bacillus, leprosy bacillus.
- M. marianum former name for M. scrofulaceum.
- M. marinum a bacterial species causing spontaneous tuberculosis in salt water fish; it also occurs in other cold-blooded animals, in some aquaria and swimming pools in which it may cause human cutaneous infection (see swimming pool granuloma), irrigation canals and ditches, and ocean beaches.
- M. microti a bacterial species causing generalized tuberculosis in voles; transmissible to guinea pig s, rabbits, and calves, causing localized infections.
- M. paratuberculosis a bacterial species causing Johne disease, a chronic enteritis in cattle.
- M. phlei a bacterial species found in soil and dust and on plants. SYN: Moeller grass bacillus.
- M. scrofulaceum a bacterial species frequently associated with cervical adenitis in children.
- M. smegmatis a saprophytic bacterial species of bacteria found in smegma from the genitalia of humans and many of the lower animals; it is also found in soil, dust, and water.
- M. tuberculosis a bacterial species that causes tuberculosis in humans; it is the type species of the genus M.. SYN: Koch bacillus, tubercle bacillus (1).
- M. ulcerans a bacterial species causing Buruli ulcers in humans; transmissible from soil, usually after an injury, and possibly by an insect vector.
- M. vaccae a rapidly growing scotochromogenic, nonpathogenic species that is distributed widely in nature.
- M. xenopi a bacterial species found in a skin lesion of a cold-blooded animal, Xenopus laevis; a rare cause of nosocomial human pulmonary tuberculosis.

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my·co·bac·te·ri·um -'tir-ē-əm n
1) cap a genus of nonmotile acid-fast aerobic bacteria of the family Mycobacteriaceae that are usu. slender and difficult to stain and that include the causative agents of tuberculosis (M. tuberculosis) and leprosy (M. leprae) as well as numerous purely saprophytic forms
2) pl -ria -ē-ə any bacterium of the genus Mycobacterium or a closely related genus
my·co·bac·te·ri·al -ē-əl adj

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a genus of rodlike Gram-positive aerobic bacteria that can form filamentous branching structures. Some species are pathogenic to animals and humans: M. leprae (Hansen's bacillus) causes leprosy; M. tuberculosis (Koch's bacillus) causes tuberculosis. M. bovis causes tuberculosis in cattle but can also infect the human lungs, joints, and intestines. M. paratuberculosis, which causes Johne's disease in cattle, can also be transmitted in milk and is suspected of being a cause of Crohn's disease.
M. tuberculosis is by far the most common species responsible for infections of the lung. Other mycobacteria that infect the lung are variously described as atypical, anonymous, or opportunistic - the favoured term since they usually require pre-existing lung damage or a defect in the patient's immunity before they can give rise to infection. The opportunistic mycobacteria that most commonly cause lung infections are M. kansacii, M. xenopi, M. malmoense, and a group known as the MAI complex (M. avium, M. intracellulare). Infections caused by all these organisms can mimic pulmonary tuberculosis but are much more difficult to treat since they are resistant to many of the antituberculosis drugs. The MAI organisms are particularly likely to cause superimposed infection in cases of AIDS.

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My·co·bac·te·ri·um (mi″ko-bak-tērґe-əm) [myco- + Gr. baktērion little rod] a large genus of bacteria of the family Mycobacteriaceae, consisting of aerobic, acid-fast, nonmotile, curved or straight rods; it includes the highly pathogenic organisms that cause tuberculosis (M. tuberculosis) and leprosy (M. leprae). The type species is M. tuberculoґsis.

Medical dictionary. 2011.

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