NTM, Auntie Em!

In this episode, Dr. Kimothy Smith and Christian Railsback discuss 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. A transcript of the conversation appears below.

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The Wee Beasties podcast is a production of Nephros, Inc., a leading water technology company providing filtration and pathogen detection solutions to the medical and commercial markets.

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SHOW TRANSCRIPT:

Christian:  I am back with Dr. Kimothy Smith. Kimothy, welcome back!

Kimothy:  Thanks, Christian.

Christian:  So, what’s our bug for today?

Kimothy:  Non-tuberculosis mycobacterium. (NTM)

Christian:  Okay, NTM. What is NTM?

Kimothy:  NTM actually 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.

Christian:  Interesting, so it seems like there could be a lot of ground to cover here.  Are there certain types of this mycobacteria that are more likely to exist in potable water and cause infections?

Kimothy:  Yes, it’s actually very complex and more than we can cover in this podcast. But, we can get a start and a little bit of a taste, so to speak, for NTM. In NTM’s, the one most likely to cause a health issue in water is called Mycobacterium avium — it is actually a complex, Mycobacterium avium complex (MAC).  It can be found in fresh and saltwater, as well as in soil or dust, too. Like Pseudomonas, these are biofilm producers, and they use this as a niche to colonize. Particularly because they can take advantage of protozoa and amoebae that are motile. MAC behave as intercellular parasites and use them to colonize.

Christian:  And at the cellular level, what kinds of characteristics stand out?

Kimothy:  Well, different from our last bug, Pseudomonas, MAC is a gram-positive bacterium and non-motile.  But it is rod-shaped, like Pseudomonas was. Perhaps one of the most notable features at the cellular level is its slow growth rate and slow cellular metabolism. Where some bacteria might reproduce every 20 minutes, the mycobacteriums are usually measured in hours, and sometimes even a day or more, for them to reproduce. So, this is really slow. 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 in a kind of wax, increasing its cellular defense – antibiotics and disinfectants can’t penetrate it as easily.

Christian: It sounds like it’s a pretty difficult bacteria to kill. Would one be able to use chloramine or superheating to address NTM in their water supply?

Kimothy:  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.   

Christian:  The bug has a waxy protective coating, a slow metabolic engine that allows it to resist antibiotics, and it’s really tolerant to chlorine and chloramine treatments.  This is an impressive set of defenses.  Is there anything else?

Kimothy:  Well, two more things, actually. Remember that I mentioned MAC produces mycolic acid as an additional protective barrier on its cell membrane? Well, that is also an essential component to the formation of biofilms, which it uses to both protect itself and enhance colonization and translocation, so when pieces of the biofilm break off. Lastly, MAC is sometimes not easy to culture because the cells enter a state of VBNC, or Viable but Non-Culturable.  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 a 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 pathogens are in your premise plumbing. So, yes, this is a really complex bug to get rid of – it has a tough cell membrane, it hides in biofilms, it can resist anti-biotics, it can survive chloramine and chlorine treatments, and it can remain undetectable in VBNC state.

Christian:  Wow, okay. How does one become infected with NTM and what are the consequences of becoming infected?

Kimothy:  MAC enters the body when individuals inhale or swallow the bacteria, say through a water source, so this could be a shower, steam rising, or drinking water. But 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 COPD or emphysema patients; very young or very old; cancer and organ transplant patients are most susceptible. Patients who are infected are not thought to be contagious at all, you can’t 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.

Christian:  Fascinating stuff, Kimothy.  Well, is there anything else before we close today?

Kimothy:  I’d just like to point out some resources, in case individuals are interested in learning more.  The CDC’s Opportunistic Pathogens of Premise Plumbing list was the inspiration for our molecular assays at Nephros.  I recommend people start there if they are wanting to know more.

Christian:  Well, again, thanks so much! This is always a pleasure.

Kimothy:  Likewise, Christian.