Last updated on May 2nd, 2021
We have already discussed the common properties and classification of Nontuberculous Mycobacteria (NTM) in the previous blog post. In this post, you can find information regarding pathogenic genera, their epidemiology and types of disease caused by them.
Mycobacterium avium-intracellularae complex (MAC): Nonphotochromogens
These Non-Tuberculous Mycobacteria (NTM) are classified as Nonphotochromogens in Runyon classification. M. avium complex was first recognized as human pathogens in the 1990s. They are an important pathogen in immunocompromised and immunocompetent populations.
They are ubiquitous in environmental sources including natural waters; soil etc. Taxonomically, the M. avium-intracellularae complex comprises M. avium, M. intracellularae, M. paratuberculosis, M. lepraemurium, and the “wood pigeon” bacillus.
These organisms cause opportunistic infections in immunocompromised patients such as individuals infected with HIV. The lungs are primarily affected, but infection can spread to other organs as well. Disseminated disease is seen in the case of AIDS patients.
NTM lung infections occur more frequently in older adults and people with other lung diseases, like bronchiectasis and chronic obstructive pulmonary disease (COPD).
Mycobacterium fortuitum complex (Rapid growers)
It is a group of free-living; rapid-growing NTM. The colonies of these organisms appear on solid media in 7 days or less. They constitute the second major group of NTM.
They have been found in soils, marshes, rivers etc. People acquire the infection when organisms gain entry into the host by inoculation into skin and subcutaneous trauma, injections, or surgery or through animal contact.
Injection site abscesses among drug users are the most common form of this disease but the pulmonary infection occurs occasionally. Infection can also be associated with implanted devices. Little is known about the pathogenesis of these organisms.
Of the potentially pathogenic, rapidly growing NTM, M. fortuitum, M. chelonae, and M. abscessus constitute approximately 97% of disease.
Mycobacterium scrofulaceum (Scotochromogens)
It is an NTM classified as Scotochromogens and is found in raw milk, soil, water, and dairy products.
It is the most common cause of granulomatous cervical lymphadenitis in children. The disease is characterized by enlarged lymph nodes, which may ulcerate or form draining sinus tracts.
Among the NTM classified as photochromogens, M. kansasii, M. marinum are the major potential pathogens. M. asiaticum, M. intermedium are found to be associated with pulmonary disease.
- Mycobacterium Kansasii
Causes chronic pulmonary disease as well as infections of the skin and subcutaneous lymph nodes.
The disease tends to progress slowly and is susceptible to usual mycobacterial drugs.
- Mycobacterium marinum
It grows at much lower temperatures than other mycobacteria (i.e. around 30°C) and is present in both fresh and saltwater. It causes nodular ulcerative lesions of the skin at the site of trauma. The infection may spread to the liver through lymphatic circulation.