Lecture 10: Mycobacteria (Focus on Tuberculosis) Flashcards
What structural features make mycobacteria unique?
Acid-fast (high lipid/mycolic acid content in cell wall).
Slow-growing (15–20 hr generation time).
Obligate aerobes, non-motile, non-sporulating.
Describe the ZN staining process and its significance.
Carbol fuchsin (hot) → all bacteria pink.
Acid-alcohol wash → only acid-fast bacteria retain stain.
Methylene blue counterstain → non-acid-fast bacteria turn blue.
Key for TB diagnosis: Detects M. tuberculosis in sputum.
How is TB transmitted, and what are the stages of infection?
Transmission: Inhalation of droplet nuclei (coughing/sneezing).
Stages:
Macrophage invasion → intracellular replication.
Granuloma formation (Ghon focus).
Latent (90%) or active (10%) TB.
Compare primary Ghon focus and secondary/reactivation TB.
Ghon focus: Healed latent lesion (calcified).
Secondary TB: Reactivation due to immunosuppression (HIV, steroids) → liquefaction → dissemination.
List key symptoms of active pulmonary TB.
Chronic cough (>3 weeks), hemoptysis, night sweats, weight loss, fever.
Extrapulmonary: Meningitis, bone/joint infections.
How is pulmonary TB diagnosed in the lab?
Microscopy: ZN stain of sputum (acid-fast bacilli).
Culture: Lowenstein-Jensen agar (4–6 weeks; buff, serpentine colonies).
PCR: Rapid detection of M. tuberculosis DNA.
What is the cord factor, and why is it important?
Trehalose dimycolate → causes serpentine growth.
Virulence factor: Inhibits WBC migration, toxic to host cells.
What is the first-line TB drug regimen?
RIPE therapy (6 months):
Rifampicin, Isoniazid, Pyrazinamide, Ethambutol.
Side effects: Hepatitis (monitor LFTs), GI upset.
How do latent and active TB differ clinically?
Latent: No symptoms, non-infectious, positive skin test/IGRA.
Active: Symptomatic, infectious, positive sputum tests.
Why is TB a major public health issue?
1.5 million deaths/year; linked to HIV, poverty, drug resistance (MDR/XDR-TB).
UK resurgence: Immigration, immunosuppression, homelessness.
