Mycobacteria Flashcards
M. tuberculosis causes…
Tuberculosis
M. avium complex (MAC) causes…
Disseminated infection in AIDS, chronic lung infection
M. kansasii causes…
Chronic lung infection
M. marinum causes…
Fish tank granuloma
M. ulcerans causes…
Buruli ulcer
Rapidly growing mycobacteria (M. foruitum complex) causes…
Skin and soft tissue infections.
M. leprae causes…
Leprosy
Tuberculosis numbers
1.5M deaths per year
2.5BN infected people
10.4M new cases per year
> 500K ABx resistance
Mycobacteria
Slightly curved, beaded bacilli.
High lipid content with mycolic acids in cell wall makes Mycobacteria resistant to Gram stain
Ziehl-Neelsen stain
- Carbol fuchsin
- Acid alcohol (AFB are resistant to de-staining)
- Methylene blue
Need 10,000 bacilli per ml sputum to diagnose
Microbiology of Mycobacteria
- Aerobic, non-spore forming, non-motile bacillus.
Cell wall has high molecular weight lipids. (Weakly gram-positive or colourless).
Cell wall characteristics
A significant part of the 4.4 Mb genome of Mtb encode genes involved in lipogenesis and lipolysis.
Mycolic acids
Lipoarabinomannan
What is the generation time for M. tuberculosis?
15-20 hours so it is a slow growing bacteria.
How is M. tuberculosis transmitted?
Air droplets.
Primary tuberculosis
Initial contact made by alveolar macrophages.
Bacilli taken in lymphatics to hilar lymph nodes.
Latent tuberculosis
Cell mediated immune response from T-cells.
Primary infection contained but CMI persists -> latent TB.
Latent TB:
- no clinical disease
- detectable CMI to TB on tuberculin skin test.
Pulmonary tuberculosis
Granulomas form around bacilli that are found in the apex.
TB may spread in lung causing causing other lesions.
Could occur immediately following primary infection (post-primary) or months later after reactivation.
Why are granulomas more common in the apex of the lung?
In apex of lung there
Is more air and less
blood supply
(fewer defending
white cells to fight).
What makes up the primary complex?
Granuloma + Lymphatics + Lymph nodes
TB can spread beyond the lungs
Bacilli in:
- lung apex
- in lymph nodes
- in bone and joint
- in pleura
- in genito urinary system
- meningitis
- Miliary TB
Tuberculosis of the spine
Gibbus formation.
Killing of Mycobacteria
Phagocytosed by macrophages and trafficked to a phagolysosomes.
The bacterium has adapted to the intracellular environment = withstand phagolysosomal killing and escapes to the cytosol.
What is required for the intracellular killing by macrophages?
Effective immunity requires CD4 T-cells which generate interferon gamma and this helps activate them.
TB-Macrophage-Trojan Horses
TB can survive inside macrophages and therefore evade the immune system.
Hallmarks of granuloma formation
If the granuloma works: Mycobacteria shut down metabolically in order to survive – dormancy.
But if fails, e.g. in the lung, this can result in the formation of a cavity full of live mycobacteria and eventual disseminated disease (consumption).
