Mycobacterium tuberculosis

Question 1

Morphology

Answer 1

mycolic acid cell envelope
does not gram stain
non-motile rods

Question 2

Classification/diagnosis

Answer 2

tuberculin skin test/mantoux/PPD
(cross-reactivity with environmental mycobacterium or BCG vaccine, false negatives in immunocomprimised or diseased)

interferon-gamma release test, sputum smear and culture, acid-fast stain, fluorochrome stain, PCR

Question 3

Pathology

Answer 3

Facultative intracellular pathogens
First infects alveolar macrophages, replicates slowly in vesicles, prevents fusion of vesicles to lysosomes, cases granulomatous inflammation and giant cells (fused macrophages to wall off pathogen)

Question 4

Epidemiology

Answer 4

2 billion worldwide infected with 10% risk of reactivation, 8 million new cases of active disease/yr
10-15 million in US with latent infection
higher risk in homeless, urban impoverished, immigrants, prisons, healthcare setting
airborne transmission by aeroslized droplet nuclei

Question 5

Diseases/Symptoms

Answer 5

Primary infection (infects alveolar macrophages, carried to lymph nodes and bloodstream)
Latent infection (asysmtomatic, not contagious)
Reactivation (occurs w/ age, stress, weakened immune system, occurs in upper lobes, apices of lun, caseous necrosis coalesce in cavities, cavitry TB highly contagious)
symptoms include cough, sputum, shortness of breth, fever, chills. fatigue, weight loss, pneumonia, miliary TB, laryngeal TB, GI TB, meningitis, lymphadenitis, renal TB, skeletal TB

Question 6

Treatment/Vaccination

Answer 6

treat active disease with directly observed therapy (DOT) with multi-drug regimen for 6 months-1 year
First line drugs (isoniazid, rifampin, ethembutol, pyraninamide)
Treat latent infection with 9 months isoniazid (INH) or 6 months rifampin
MDR-TB and XDR-TB increasin, many countries still use BCG vaccine