Mycobacterium Tuberculosis Flashcards
Major component of MTB cell wall?
Mycolic Acid, lipid rich, so resistant to traditional stains/antibiotics.
What contributes to clumping of MTP?
Hydrophobicity
What is the incubation time of MTB?
Very slow, 12-24 hours. Takes about 4-6 weeks to visualize colonies.
Characteristics of MTB
Non-motile, non spore-forming aerobic bacilli. Gram null but stain with an acid fast stain.
Virulence factors
No toxins or capsules, just intracellular survival. Inhibition of phagosome-lysosome system
Natural history of MTB
Transmission, primary tuberculosis with cavitary lesions, then latent TB, can reactivate.
How is MTB spread?
Small droplet nuclei that can remain suspended in air for several hours. These penetrate alveoli and are ingested by alveolar macrophages
What happens to start primary infection?
Spread to hilar lymph nodea
How does latent TB occur?
Immune system contains primary infection and a granuloma is formed. MTB persist within inactivated macrophages within the granuloma.
Ghon complex
Hilar lymph node caseation and subpleural granulomas.
Latent TB is the endpoint of primary tb in ?% of patients
90%
Are patients with latent TB contagious?
No.
How to diagnose latent TB?
PPD or IGRA. IGRA not affected by the BCG vaccination.
How to treat latent TB?
Isoniazid for 9 mos.
What is the key histological sign of MTB?
Caseating granulomas (caseous necrosis)
Symptoms of active TB
Cough, hemoptysis, night sweats, anorexia, weight loss, weakness, dyspnea.
Does TB only occur in the lung?
No, can occur in bones, LNs, brain, GI tract, kidneys, etc.
Miliary vs cavitary TB
Miliary is nodular, cavitary is cavitary
How to stain TB?
Acid-fast
Pott’s disease?
Vertebral body TB
TB drug regimen
Rifampin, Isoniazid, Pyrazinamide, Ethambutol for 2 months, then RIF and INH for 4.
Rifampin
Inhibits DNA-dep RNA pol, induces hepatic p450 enzymes. Hepatotoxicity, thrombocytopenia.
Isoniazid
Prodrug that blocks mycolic acid synthesis. Hepatoxic.
Ethambutol
blocks polysaccaride synthesis in cell wall.
