Micro 10 - Mycobacteria Flashcards
What is the difference between Ghon focus and Ghon complex?
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.
What does Tuberculin Positive mean?
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.
What does Tuberculin negative mean?
No infection or anergic (no immune response) like people on steroids, malnutrion, immunocompromised states, sarcoidosis.
What is secondary TB?
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).
What is extrapulmonary TB?
It can go to CNS lesions, parenchymal tuberculoma, meningitis, vertebra (Pott’s disease), lymphadenitis, renal disease, GI disease, Miliary TB.
What culture and how long does it take to grow mycobacteria?
They are G(+) acid-fast organism that require 2-4 weeks to culture in Lowenstein-Jensen agar.
How do we quickly diagnose TB?
Acid-fast stain on sputum of the patient for 3 days in a row.
What is the treatment for latent TB?
It is 6-9 months of isoniazid (INH).
What is the treatment for primary or secondary TB?
Multi-drug regimen.
[RIPE]
Rifampin, Isoniazid, Pyrazinamide, Ethambutol. Take for 2 months, then continue INH and rifampin for another 4 months.
What does Mycobaterium kansasii cause?
Pulmonary TB-like symptoms. Prevalent in patients with chronic bronchitis or emphysema.
What does Mycobacterium avium intracellulare (MAI) cause?
AKA Mycobaterium avium complex (MAC), most commonly seen in AIDS patients. Causes fever, diarrhea, malabsorption, and affect bone marrow.
What antibiotic is used for prevention of MAI in AIDS patients? When should this prophylaxis begin?
Azithromycin when CD4 is below 50.
Where do we see Mycobacterium marinum cases?
Aquatic-associated mycobacterium, seen in shipyards and acquiarium workers.
What causes Leprosy (Hansen disease)?
Caused by the Mycobacterium leprae. It is an acid-fast bacillus. It likes to affect the peripheral nerves and mucosa.
What are the two types of leprosy?
Lepromatous and tuberculoid.
What is the treatment for Lepromatous type?
Dapsone, rifampin, and clofazimine for 24 months.
What is the treatment for Tuberculoid type?
Dapsone and rifampin for 12 months.
What side effect does Dapsone cause?
Hemolysis in G6PD deficient patients.
What is the mechanism of Isoniazid (INH)?
Inhibits the synthesis of mycolic acid. Only agent used in solo prophylaxis against TB.
How can we prevent the neurotoxic effect of Isoniazid?
By concurrently giving Pyridoxine (vitamin B6).
What are the side effects of Isoniazid?
Neurotoxic (prevented with Vit B6), hepatotoxicity and can cause drug-induced lupus.
What is the mechanism of Rifampin?
[4 Rs of Rifampin]
RNA polymerase inhibitor, Revs up microsomal P450, Red-Orange body fluids, Rapid Resistance if used alone.
In what disease do we use Rifampin?
TB, Leprosy, Meningitis prophylaxis (N.meningitidis, H.influenzae type B).
What is the mechanism of action of Pyrazinamide?
Inhibit mycolic acid production by blocking mycobacterial pyrazinamidase.
What are the side effects of Pyrazinamide?
Hyperuricemia and Hepatotoxicity.
What is the mechanism of action of Ethambutol?
Decrease carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase.
What are the side effects of Ethambutol?
Optic Neuropathy: Red-green color blindness (reversible).
RFF: Calcified granuloma in the lung, plus hilar lymphadenopathy.
Ghon complex.
RFF: Back pain, fever, night sweats, and weight loss.
Pott’s disease.
RFF: Standard treatment for TB.
[RIPE]
Rifampin, Isoniazid, Pyrazinamide, Ethambutol.
What are the characteristics of Primary TB?
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.
