Chronic Pneumonia

The disease is more commonly known as TB. It is most commonly caused by Mycobacterium tuberculosis, but others of the same genus also cause TB.

M. bovis is found in humans and cattle and infect the lungs. M. ulcerans affects the skin and is found only in humans. M. leprae causes leprosy, and can only grow inside cells so we still have no medium to grow it in the lab.

There are a bunch of mycobacteria with low virulence that are environmental. They are found in the soil and water, but they have a very high critical mass, so they rarely used to cause disease. Today, because of AIDS and other breakdowns of cell-immunity, we see 50% of pneumonia due to these bacteria. They are called PPEM (Potential Pathogenic Environmental Bacteria).

The mycobacterium cell wall is very lipidic. They have fatty acids on the surface with very long chains. Most cells have about 16 linked carbons. Mycobacteria have 60-120 carbons linked to mycolic acid. The bacteria also have a peptidoglycan layer and then on top lipoarabinomaman linked to cord factor.

What’re the common characteristics of all mycobacteria?

1. Gram +

2. Acid fast + (Zeihl Nelson) – heat fix the first stain so all bacteria on the slide are red. Decolorize with acid, and only the mycobacteria will retain the color. Counter stain blue so all other bacteria are now blue.

3. Lipidic cell wall makes bacteria resistant to disinfectants, alkaline and acidic environments, dryness, and conventional antibiotics, but Isoniazide and Rifampin usually work.

4. Strict aerobes

5. Long generation time – 2 weeks to see a colony form

6. Hide in phagocytes, shut down the antimicrobial systems, multiply, and burst, but can also multiply outside phagocyte.

7. The lesion in the lungs is characterized by caseous necrosis.

What is the mechanism of infection?

1. Droplet infection (also by inhaling dust)v

2. Gets into lungs (can’t survive in throat)b

3. Multiply relatively fast

4. Burst outta cell

5. Cause caseous necrosis t

6. Liquify tissue y

7. Cavity in lungs u

8. (Remains asymptomatic in many cases, but if it gets into the lymph node and then to the blood it can infect the liver and kidney and has a high mortality.)

9. The bacteria become dormant because the growth slows almost to 0, and cell mediated immunity is developed o

10. Eradication or reactivation

What’s up with the dormant bacteria?

Well proteins released by the bacteria cause T-cell activation. Cytokines are released which activate macrophages. The TB is slowed down or even completely eradicated.

Mantoux test  PPD (Partially Purified protein Derivative) is injected under the skin and if the person has antibodies to TB, a delayed hypersensitivity reaction happens and you can see a bump in the skin.

If a person who has the dormant TB now somehow compromises his immune system (AIDS, immunosuppressive drugs, addiction) the bacteria can reactivate and infect. When the bacteria start multiplying at an intermediate rate, epitheliod cells and lymphocytes accumulate around the lesion to prevent spreading. This is called granulation. More and more granulation leads to death.

Features of TB cause by PPEM:

1. The frequency of exposure to bacteria is high

2. Most infections are from water

3. Intestinal and respiratory colonization common

4. TB in patients with compromised immunity

5. Pulmonary disease predominantly in white males over 45 with preexisting pulmonary disease

Category: Medicine Notes