Micro 10 - Mycobacteria

Question 1

What is the difference between Ghon focus and Ghon complex?

Answer 1

Ghon focus is primary lesion in the mid to lower zones of the lung. Usually a small area of granulomatous inflammation. When they calcify, we can see it on CXR. Ghon complex is when the patient has a hilar lymph node and a Ghon focus on CXR.

Question 2

What does Tuberculin Positive mean?

Answer 2

Means that you are positive in the PPD (purified protein derivative) skin test. Means that there is a current infection, past exposure or BCG vaccine.

Question 3

What does Tuberculin negative mean?

Answer 3

No infection or anergic (no immune response) like people on steroids, malnutrion, immunocompromised states, sarcoidosis.

Question 4

What is secondary TB?

Answer 4

Primary TB infection, then recovered to latent phase, then reactivated. This stage is where we see fibrocaseous cavitary lesion (cheese-like caseous necrosis) and more symptoms (fever, hemoptysis, weight loss, night sweats).

Question 5

What is extrapulmonary TB?

Answer 5

It can go to CNS lesions, parenchymal tuberculoma, meningitis, vertebra (Pott’s disease), lymphadenitis, renal disease, GI disease, Miliary TB.

Question 6

What culture and how long does it take to grow mycobacteria?

Answer 6

They are G(+) acid-fast organism that require 2-4 weeks to culture in Lowenstein-Jensen agar.

Question 7

How do we quickly diagnose TB?

Answer 7

Acid-fast stain on sputum of the patient for 3 days in a row.

Question 8

What is the treatment for latent TB?

Answer 8

It is 6-9 months of isoniazid (INH).

Question 9

What is the treatment for primary or secondary TB?

Answer 9

Multi-drug regimen.
[RIPE]
Rifampin, Isoniazid, Pyrazinamide, Ethambutol. Take for 2 months, then continue INH and rifampin for another 4 months.

Question 10

What does Mycobaterium kansasii cause?

Answer 10

Pulmonary TB-like symptoms. Prevalent in patients with chronic bronchitis or emphysema.

Question 11

What does Mycobacterium avium intracellulare (MAI) cause?

Answer 11

AKA Mycobaterium avium complex (MAC), most commonly seen in AIDS patients. Causes fever, diarrhea, malabsorption, and affect bone marrow.

Question 12

What antibiotic is used for prevention of MAI in AIDS patients? When should this prophylaxis begin?

Answer 12

Azithromycin when CD4 is below 50.

Question 13

Where do we see Mycobacterium marinum cases?

Answer 13

Aquatic-associated mycobacterium, seen in shipyards and acquiarium workers.

Question 14

What causes Leprosy (Hansen disease)?

Answer 14

Caused by the Mycobacterium leprae. It is an acid-fast bacillus. It likes to affect the peripheral nerves and mucosa.

Question 15

What are the two types of leprosy?

Answer 15

Lepromatous and tuberculoid.

Question 16

What is the treatment for Lepromatous type?

Answer 16

Dapsone, rifampin, and clofazimine for 24 months.

Question 17

What is the treatment for Tuberculoid type?

Answer 17

Dapsone and rifampin for 12 months.

Question 18

What side effect does Dapsone cause?

Answer 18

Hemolysis in G6PD deficient patients.

Question 19

What is the mechanism of Isoniazid (INH)?

Answer 19

Inhibits the synthesis of mycolic acid. Only agent used in solo prophylaxis against TB.

Question 20

How can we prevent the neurotoxic effect of Isoniazid?

Answer 20

By concurrently giving Pyridoxine (vitamin B6).

Question 21

What are the side effects of Isoniazid?

Answer 21

Neurotoxic (prevented with Vit B6), hepatotoxicity and can cause drug-induced lupus.

Question 22

What is the mechanism of Rifampin?

Answer 22

[4 Rs of Rifampin]

RNA polymerase inhibitor, Revs up microsomal P450, Red-Orange body fluids, Rapid Resistance if used alone.

Question 23

In what disease do we use Rifampin?

Answer 23

TB, Leprosy, Meningitis prophylaxis (N.meningitidis, H.influenzae type B).

Question 24

What is the mechanism of action of Pyrazinamide?

Answer 24

Inhibit mycolic acid production by blocking mycobacterial pyrazinamidase.

Question 25

What are the side effects of Pyrazinamide?

Answer 25

Hyperuricemia and Hepatotoxicity.

Question 26

What is the mechanism of action of Ethambutol?

Answer 26

Decrease carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase.

Question 27

What are the side effects of Ethambutol?

Answer 27

Optic Neuropathy: Red-green color blindness (reversible).

Question 28

RFF: Calcified granuloma in the lung, plus hilar lymphadenopathy.

Answer 28

Ghon complex.

Question 29

RFF: Back pain, fever, night sweats, and weight loss.

Answer 29

Pott’s disease.

Question 30

RFF: Standard treatment for TB.

Answer 30

[RIPE]

Rifampin, Isoniazid, Pyrazinamide, Ethambutol.

Question 31

What are the characteristics of Primary TB?

Answer 31

Mostly asymptomatic, can have weak fever, chest pain and cough. Usually CXR is normal but can show hilar adenopathy. Can show Ghon focus and Ghon complex.