Nontuberculous Mycobacteria

Non-tuberculous mycobacteria (NTM) have been known almost as long as M. tuberculosis itself, but their clinical significance was not recorded until the 1950s.

The term "nontuberculous mycobacterioses", or "NTM" for short, refers to a heterogeneous group of more than 190 environmental mycobacteria characterized by a wide diversity in terms of their occurrence and adaptation to environmental conditions. The reference to the obligate pathogenic mycobacterial species of tuberculosis and leprosy is reflected in the antipodal naming "nontuberculous mycobacterioses."

NTMs are facultatively humpathogenic and can become clinically relevant as opportunistic pathogens, under certain conditions, some nosocomially, especially in immunocompetent but also in immunocompetent individuals. Some clearly definable dermatological clinical pictures such as "swimming pool granuloma" and "Buruli ulcer" refer to defined pathogens such as M. marinum and M.ulcerans. Other NTM infections are not very characteristic with regard to their clinical-dermatological symptoms, so that their assignment often turns out to be a microbiological incidental finding.

So far, > 190 different NTM species have been discovered; more will follow. In addition to the NTMs that have also been detected in environmental samples, there are species such as M. ulcerans, M. marinum, M. genavense or M. haemophilum that are significantly more host-specific than other species. Infections of birds have been described for M. genavense. However, there is no evidence of spread outside this host.

Mycobacterium ulcerans, the causative agent of Buruli ulcer, has been diagnosed in over 33 countries worldwide, not only in tropical areas of West Africa but also in areas with temperate non-tropical climates, including Australia and Japan. In temperate areas of Australia, M. ulcerans infections are also known (Bairnsdale ulcer). The pathogen has also been detected in mosquitoes (Aedes camptorhynchus/ Johnson PD et al. 2007).

For M. haemophilum, water reservoirs are considered a probable source of infection.

For M. marinum , fish and seafood. Skin lesions occur at the site of inoculation as granulomatous, mostly verrucous plaques or nodules, untreated also as sporotrichoid cutaneous-subcutaneous nodules.

M. intermedium: can cause granulomatous dermatitis. Cases have been reported in which M. intermedium was transmitted by contaminated water from whirlpools (Edson RS et al. 2006).

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Basically, non-tuberculous mycobacteria can be divided into:

• slow-growing NTM
• and
• fast-growing NTM

Furthermore, a subdivision can be made on the basis of their pigment production according to:

• photochromogenic
• scotochromogenic
• or non-pigmented.

These subdivisions have no major significance for the clinician.

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Slow-growing NTM:

The list of clinically important slow-growing nontuberculous mycobacteria (NTM) is constantly expanding as new species are identified and older ones are recognized as pathogenic. Some NTMs are not newly discovered, but were previously thought to be virtually non-pathogenic. In the past, many of them were considered contaminants when isolated from clinical samples. Since they are ubiquitous in nature, many NTM are isolated from ground or tap water, soil, house dust, domestic and wild animals and birds. Most infections occur by inhalation or direct inoculation from environmental sources.

• M. arupense
• M. asiaticum
• M. avium*
• M.-avium complex (consists of 12 validly published species based on molecular criteria:Mycobacterium avium

  ,Mycobacterium intracellulare, Mycobacterium chimaera, Mycobacterium colombiense, Mycobacterium arosiense, Mycobacterium vulneris, Mycobacterium boucheduronense, Mycobacterium timonens, Mycobacterium marseillnse, Mycobacterium yongoense, Mycobacterium paraintracellulare, Mycobacterium lepraemurium).

• M. bohemicum
• M. branderi
• M. celatum (pulmonary infections, especially in immunocompetent patients)
• M. chimaera
• M. europaeum
• M. florentinum
• M. genavense
• M. gordonae
• M. haemophilum
• M. heckeshornense
• M. interjectum
• M. intermedium
• M. intracellulare*
• M. kansasii
• M. cubicae
• M. lentiflavum
• M. malmoense
• M. marinum
• M. nebraskense
• M. palustre
• M. saskatchewanse
• M. scrofulaceum
• M. shimodei
• M. simiae
• M. szulgai
• M. terrae complex
• M. ulcerans
• M. vulneris*(infected wounds e.g. after dog bites)
• M. xenopi

* belonging to the M. avium complex

Fast-growing NTM: The eponymous characteristic of fast-growing mycobacteria is that they show significant growth in less than 7 days at their optimal growth temperature. This statement refers only to standard culture conditions. Fast-growing mycobacteria are clearly resistant to a wide range of environmental conditions. They are therefore widespread (Falkinham 3rd JO 2009).

• M. abscessus** (after cosmetic procedures, other nosocomial transmissions)
• M. alvei
• M. aurum
• M. boenickei
• M. brumae
• M. chelonae**
• M. confluentis
• M. elephantis
• M. fortuitum complex**(M. abscessus, M. fortuitum, M. chelonae).
• M. goodii (catheter-associated nosocomial infections)
• M. holsaticum
• M. immunogenum (more frequent after cosmetic procedures, other nosocomial transmissions)
• M. iranicum sp. nov.
• M. margeritense
• M. mucogenicum
• M. peregrinum
• M. phocaicum
• M. septicum (phlegmonous skin infections after cosmetic surgery; pneumonia)
• M. thermoresistible

** Belonging to the M. fortuitum complex

See also non-tuberculous mycobacterioses. Transmission from person to person does not occur.

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