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I am not sure which word is the best here for colonisation of alveoli by acid fast-mycobacteria. I found this question, and I am getting confused by the term obstruction of alveoli because I tend to relate it to COPD which is not a case here:

Which of the following is the predominant pathogenic mechanism of tuberculosis?

  • a) cell-mediated hypersensitivity
  • b) obstruction of alveoli by large number of acid-fast mycobacteria

I think the right answer is "obstruction of alveoli by large number of acid-fast mycobacteria", but I am not sure if you can say that acid-fast mycobacteria obstruct alveoli.

Are acid-fast mycobacteria "obstructing" alveoli or just colonizing?

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1 Answer

up vote 2 down vote accepted

Mycobacteria are on the order of 2µm in length and 0.2µm in diameter. Alveoli are on the order of 200µm in diameter. Obstruction is possible, but M. tuberculosis grows rather slowly. Too slowly, in fact, to avoid being engulfed by alveolar macrophages.

Furthermore, obstruction does not sufficiently explain the predominant symptoms of tuberculosis: bloody sputum and the tubercles themselves.

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I certainly agree it's not the myco colony obstructing the alveoli, but rather the elicited immune response does a pretty good job of that. Muc5, Il13, etc are all slamming in to cause mucin production and inflammation. –  Atl LED Aug 22 '13 at 20:25
    
Thank you for your clear answer! So obstruction is possible and it is mostly theoretical model by large number of acid-fast mycobacteria. However, can we still say that obstruction of alveoli by large number of acid-fast mycobacteria is the predominant pathogenic mechanism of tuberculosis? –  Masi Aug 22 '13 at 20:26
    
@AtlLED Is this "cell-mediated hypersensitivity" more right answer? Or what would you say is the predominant pathogenic mechanism? –  Masi Aug 22 '13 at 20:27
    
To answer this homework question, consider "What causes tubercle formation?" en.wikipedia.org/wiki/Tuberculosis –  Gossar Aug 22 '13 at 20:32
    
"In most forms of the disease, the bacillus spreads slowly and widely in the lungs, causing the formation of hard nodules (tubercles) in the respiratory tissues and form cavities in the lungs." So the answer must be B, because it implies that bacillus is causing it as a factor. Great! Thank you! –  Masi Aug 25 '13 at 17:43
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