Published on March 9, 2014
Non-tuberculous mycobacteria Dr. Pendru Raghunath Reddy
Mycobacteria other than mammalian tubercle bacilli, which may occasionally cause human disease are called ‘non-tuberculous mycobacteria’ Other names include atypical mycobacteria, anonymous, unclassified Mycobacteria and Mycobacteria other than M. tuberculosis (MOTT)
Runyoun classification NTM have been categorized into four groups by Runyoun (1959) based on pigment production and the growth rate 1. Photochromogenes 2. Scotochromogens 3. Non-photochromogens 4. Rapid growers
Runyon Group Number Group Name Description I Photochromogens Colonies of NTM that develop pigment following exposure to light after being grown in the dark and take more than 7 days to appear on solid media II Scotochromogens Colonies of NTM that develop pigment in the dark or light and take more than 7 days to appear on solid media III Nonphotochromogens Colonies of NTM that are nonpigmented regardless of whether they are grown in the dark or light and take more than 7 days to appear on solid media IV Rapid-growers Colonies of NTM that appear on solid media in less than 7 days
They are not usually transmitted from person to person Source of infection is water, soil, food and animals Human infection with NTM is common in some areas, disease is rare Exhibits dysgonic growth on LJ medium Niacin and nitrate reduction tests are negative Not able to cause progressive disease in guniea pigs
Photochromogens The important species in this group are M. kansasii, M. marinum and M. simiae M. kansasii M. kansasii causes chronic pulmonary disease resembling tuberculosis It may also occasionally cause infections of the cervical lymphnodes, penetrating wound infections and granulomatous synovitis It can produce generalized infection in HIV patients
Mycobacterium marinum Causes a warty skin lesion known as swimming pool or fish tank granuloma Closely resembles M. kansasii but can be differentiated by its poor growth at 370C, negative nitratase, and positive pyrazinamide hydrolase
Fish tank granuloma
Scotochromogens These strains form pigmented colonies (yellow-orange-red) even in the dark They are widely distributed in the environment and sometimes contaminate cultures of tubercle bacilli
Important species in this group: M. scrofulaceum may cause scrofula (cervical adenitis) in children M. gordonae often found in tap water is a common contaminant in clinical specimens and a rare cause of pulmonary disease M. szulgai, an uncommon cause of pulmonary disease and bursitis It is a scotochromogen when incubated at 370C but a photochromogen at 250C
Scrofula (cervical adenitis)
Non-photochromogens Medically important species in this group are M. avium, M. intracellulare, M. xenopi and M. ulcerans M. avium Which causes natural tuberculosis in birds and lymphadenopathy in pigs, is one of the most common opportunistic human pathogens M. intracellulare Is commonly known as Battey bacillus
M. avium and M. intracellulare are so similar that that they have been considered as one group, the M. avium complex (MAC) MAC complex cause lymphadenopathy, pulmonary lesions or disseminated disease, particulary in AIDS patients M. xenopi, originally isolated from toads, may occasionally cause chronic lung disease in human beings M. ulcerans cause buruli ulcer
Rapid growers This is a heterogeneous group of mycobacteria capable of rapid growth, colonies appearing within 7 days of incubation at 370C or 250C Within the group, photochromogenic, scotochromogenic, and non-chromogenic species occur Most of these are purely are environmental saprophytes
The medically important species are M. fortuitum and M. chelonae M. fortuitum and M. chelonae occasionally cause pulmonary or disseminated disease but are principally responsible for postinjection abscesses and wound infections Outbreaks of abscesses following injections of vaccines contaminated by these mycobacteria have been reported
Lesions produced by NTM 1. Localized lymphadenitis 2. Skin lesions (Postinjection abscesses, swimming pool granuloma and buruli ulcer) 3. Tuberculosis-like pulmonary lesions 4. Disseminated disease
Swimming pool granuloma It is caused by M. marinum and is also known as fish tank granuloma M. marinum occurs as a saprophyte in fresh or salt water Human infection originates from contaminated swimming pools or fish tanks The bacilli enter scratches and abrasions and cause warty lesions similar to those seen in skin tuberculosis
The lesion, beginning as a papule and break down to form an indolent ulcer The disease is usually self-limiting although chemotherapy with minocycline, cotrimoxazole or rifampicin with ethambutol hastens its resolution
Buruli ulcer This disease is caused by M. ulcerans The name is derived from the Buruli district of Uganda where a large outbreak was extensively investigated Ulcers are usually seen on the legs or arms and are believed to follow infection through minor injuries After an incubation period of a few weeks, indurated nodules appear, which break down forming indolent ulcers which slowly extend under the skin When the immunoreactive phase sets in ulcers heal with disfiguring scars
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