Mycobacterium Avium complex (MAC) and Non-tuberculous Mycobacteria (NTM) are a diverse group of closely related bacteria. Although in the same family as Mycobacterium tuberculosis they do not cause tuberculosis.
The structure of the Mycobacteria cell wall is an important difference between MAC / NTM and other bacteria we commonly find in water systems. Unlike many other bacteria the cell wall of MAC / NTM is thick and rigid. This wall is coated with a waxy layer which reduces the entry of chemicals into the cell. MAC / NTM are slow growing and laboratory culture can take up to six weeks to isolate them. The combination of a relatively impermeable cell wall and slow growth rate makes disinfection more challenging than for other bacteria. It takes exposure to disinfectants for substantial periods to allow for penetration into the cell and to prevent reproduction. These same factors make antibiotic treatments equally challenging. Like Legionella they are also temperature tolerant and can multiply inside amoebae.
Building Water Systems
Several studies have shown them to be common occupants of building water systems often co-existing with Legionella. It has also been shown that Mycobacteria may be more of a challenge to water treatment than Legionella and other bacteria. Biofilms in water systems are their major breeding ground. Contaminated water is the cause of both chronic and fatal disease in health care settings. So a comprehensive risk management plan needs to take into account these bugs and their complex ecology.
Disease from Mycobacteria
MAC / NTM cause a wide range of disease usually in children or those with compromised immune systems. So like Legionella they are opportunist pathogens that can grow inside cells. This means that they are not reliant on causing infection to survive and multiply. In the environment they survive and multiply independently. Like other opportunist infections disease does not easily pass from person to person. Instead it usually comes from direct contact with a contaminated source.
The disease presentations include lung infections, skin lesions, abscesses, and lymph node infections. Some evidence suggests they may be associated with irritable bowel syndrome (Crohns’ disease). Because of this wide range of possible infections the susceptible population is also broader than Legionella.
This variety of exposure routes causes a wide range of infections. Ingestion, wound exposures, aspiration or inhalation of aerosols from contaminated water are all possible routes of infection. Therefore providing safe water to susceptible populations is the major intervention in preventing disease.
Whiley et al (2012) Mycobacterium Avium Complex – The role of potable water in disease transmission. J, Appl. Microbiol. 113(2): 223-32. https://www.researchgate.net/publication/223983969_Mycobacterium_avium_complex-The_role_of_potable_water_in_disease_transmission
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