5. A bit more on Mycobacterium tuberculosis avoidance of phagosomal killing As y

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5. A bit more on Mycobacterium tuberculosis avoidance of phagosomal killing As you learned in class, Mycobacterium tuberculosis is an intracellular bacterial pathogen that allows itself to be phagocytosed by macrophages and neutrophils, but then is able to escape killing in the phagosome, and thus establish a replicative niche there. You saw that one trick MTb has is an ability to eject or exclude VATPase from the phagosomal membrane, even though the phagosomes they inhabit do acquire some lysosomal proteins. This ability explains the impaired acidification of phagosomes that contain MTb that we saw in class. As I mentioned in class, and as you have seen here, this is not the only mechanism MTb has to survive the phagosomal environment, as acidification on its own is not highly microbicidal. 5a. Here is another Figure from the Chan et al 1992 paper (J. Exp. Med. 175:11). Again we are examining suppression of MTb growth, and again in culture (no macrophages here). In your own words,£ compare the susceptibility/resistance of MTb with the control microbe (Leishmania donovi) to H202 100 80 L. donovani -40 20 5b. H202 can be purchased in a bottle, or generated in a phagosome. What is the name of this molecule, and how is it generated in a macrophage phagosome? 0 100 200 300 400 500 600 700 H202(nmoles/120 min) Figure 5 2 x 10 cells of M. tuberculosis and L. donovani were incubated with H202 at the indicated concentration for 120 minutes in Ringer's phosphate glucose solution (pH 5.0) Microbial viability was quantified by metabolic labeling wit [H]uracil, and the inhibitory effect was measured by the % decrease in [H incorporation. 5c. What is the highest concentration of H202 that the MTb were exposed to in this experiment? Express the concentration in mmol, mol, and nmol.

Explanation / Answer

Answer:

1. Compare the susceptibility /resistance of MTb with the control microbe (Leishmania donovi) to H2O2

2. What is the name of this molecule (H2O2), and how is it generated in a macrophage phagosome?

3. What is the highest concentration of H2O2 that the MTb were exposed to in this experiment? Express the concentration in mmol, umol, and nmol.

.4. Comparing NADPH oxidase (phox) and Nitric Oxide Synthase, which is more important in controlling MTb proliferation in lung macrophages?

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