This article looks at Non-tuberculosis Mycobacterium (NTM) and how it differs from a gram-negative bacterium, like Pseudomonas. Cell structure, metabolic Mycobacterium avium performance, exploiting biofilms, and culturable but non-viable cells are among the high points on the pathogen odyssey today.
What is Non-tuberculosis Mycobacterium?
Non-tuberculosis Mycobacterium (NTM) includes 125 different species of mycobacteria. Essentially all of the mycobacteria that do not cause tuberculosis or leprosy, also known as Hansen’s disease, are included in the NTMs.
In NTMs, the ones most likely to cause a health issue in water is called Mycobacterium avium. It is a complex, Mycobacterium avium complex (MAC). It can be found in fresh and salt water, as well as in soil or dust. Like Pseudomonas, these are biofilm producers, and they use this as a niche to colonize because they can take advantage of protozoa and amoebae that are motile. MAC behave as intercellular parasites and use them to colonize.
Different from our last bug, Pseudomonas, MAC is a gram-positive bacterium and non-motile. It is rod-shaped, like Pseudomonas. Perhaps one of the most notable features at the cellular level is its slow growth rate and cellular metabolism. Where some bacteria might reproduce every 20 minutes, the Mycobacterium’s reproduction rates are usually measured in hours, and sometimes even days. This is noteworthy because it allows the bacterium to gradually uptake and process any antibiotics and disinfectants in its habitat, resulting in the bug being very resilient in an environment treated with antimicrobial agents. It also produces mycolic acids that coat the cell surface, increasing its cellular defense, meaning antibiotics and disinfectants cannot penetrate it as easily.
Many remediation methods are not effective in removing NTM from building plumbing. In fact, some remediation methods may remove competing microbes and result in increased concentrations of NTM in the water. So, they take advantage of the depression of the other bacteria in the community, and they fill that void. Still other methods such as treating water with chlorine or chloramine are ineffective, too. A study from 20151 pointed out that MAC was 500 times more resistant to chlorine than E. Coli and 40 times more tolerant to chloramine than Pseudomonas.
MAC is sometimes not easy to culture because the cells enter a state of viable but non-culturable (VBNC). This is usually because several treatment modalities have been used in the water or nutrients are in short supply, so the cell operates in a dormant, but still viable condition. This is one of those worst-case scenarios because when you send samples to a lab to be cultured there is no indication of pathogens lurking in your premise plumbing. This is a complex bug to rid of, as it has a tough cell membrane, it hides in biofilms, it can resist antibiotics, it can survive chloramine and chlorine treatments, and it can remain undetectable in VBNC state.
1 Falkinham JO III, Hilborn ED, Arduino MJ, Pruden A, Edwards MA. 2015. Epidemiology and ecology of opportunistic premise plumbing pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. Environ Health Perspect 123:749–758; http://dx.doi.org/10.1289/ehp.1408692
Patient risk associated with Non-tuberculosis Mycobacterium
One becomes infected with NTM when MAC enters the body upon inhaling or swallowing the bacteria. Most people, however, will not become ill or acquire an infection if they have healthy immune systems. Those at greatest risk for infection are individuals with compromised immune systems. Mostly, patients acquire progressive respiratory distress that eventually leads to an acute pulmonary infection. People with HIV/AIDS for example or emphysema patients, the very young or very old, cancer and organ transplant patients are most susceptible. Patients who are infected are not thought to be contagious, and you cannot pass this infection by touching or being within proximity of an infected person. Although the lungs are the most likely organ system to be affected, MAC can also affect the integumentary and lymphatic systems, resulting in lesions and inflammation.
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