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2a- Microbiology > Mycobacteria > Flashcards

Mycobacteria Flashcards

1
Q

What do mycobacteria stain as?

A

Ziehl-Neelsen positive

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2
Q

What disease does M. tuberculosis cause?

A

Tuberculosis

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3
Q

What disease does M. avium complex (MAC) cause?

A

Disseminated infection in AIDS, chronic lung infection

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4
Q

What disease does M. kansasii cause?

A

Chronic lung infection

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5
Q

What disease does M. marinum cause?

A

Fish tank granuloma

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6
Q

What disease does M. ulcerans cause?

A

Buruli ulcer

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7
Q

What disease does rapidly growing mycobacteria (M. fortuitum complex) cause?

A

Skin and soft tissue infections

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8
Q

What disease does M. leprae cause?

A

Leprosy

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9
Q

What is the shape of mycobacteria?

A
  • Rod shaped
  • Slightly curved, bacillus
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10
Q

Why doesn’t mycobacteria stain with gram stains?

A
  • High lipid content with mycolic acids in cell wall makes mycobacteria resistant to Gram stain
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11
Q

What are the properties of the cell wall of mycobacteria?

A
  • High molecular weight lipids
    • Weakly gram-positive or
      colourless
    • Survive inside macrophages,
      even in low pH environment
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12
Q

What are the properties of mycobacteria?

A

Aerobic, non-spore forming, non motile bacillus

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13
Q

What are the challenges of diagnosing tuberculosis?

A
  • Slow growing
  • Slow reproduction
  • Slow response to treatment
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14
Q

What is the growth rate of tuberculosis?

A

M. tuberculosis generation time 15-20h vs. 1h for common bacterial pathogens

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15
Q

What makes using drugs difficult for TB?

A

Thick lipid rich cell wall making immune cell killing and penetration of drugs challenging

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16
Q

How is TB spread?

A
  • Transmission through sputum
    • Air droplets
17
Q

Describe what happens in primary TB

A
  • Initial infection
  • Remains contained
  • Initial contact made by alveolar macrophages
  • Bacilli taken in lymphatics to hilar lymph nodes
18
Q

Describe what happens in latent TB

A
  • In immunocompromised people
  • Cell mediated immune (CMI) response from T-cells
  • Macrophages bring into apex of lung → triggers T cell response causing localised infection
  • Could stay in state for decades
  • Primary infection contained but CMI persists
  • No clinical disease
  • Detectable CMI to TB on tuberculin skin test
19
Q

What happens in pulmonary TB?

A
  • Latent TB can develop into
  • Infection in the apex of the lung
  • Granulomas form around bacilli that have settled in apex
  • In apex of lung, more air less blood so less WBCs
  • TB may spread in lung causing other lesions
  • Could occur immediately following primary or months later
  • Necrosis results in abscess forming and caseous material being coughed up
20
Q

Where could TB spread to and cause?

A
  • TB meningitis
  • Miliary TB (all around the place)
  • Pleural TB
  • Bone and joint TB
21
Q

What do macrophages do to mycobacteria?

A
  • Mycobacteria are phagocytosed by macrophages and traffic to a phagolysosomes
  • The bacterium has adapted to the intracellular environment and aims to withstand phagolysosomal killing and escape to the cytosol
    • May not do every time but has the machinary to do so
22
Q

What do CD4 T cells do to mycobacteria?

A
  • Effective immunity requires CD4 T-cells which generate interferon gamma and this helps activate intracellular killing by macrophage
  • Generate pro-inflammatory cytokines (interferon gamma)
  • Need cooperation between macrophages and T cells to control mycobacteria
23
Q

What leads to granuloma formation?

A
  • TB uses macrophages as Trojan Horses
  • To drag mycobacteria out of alveoli in lungs to tissues
  • Leads to granuloma formation
  • Signals to immune cells to form granulomas
24
Q

What is important for keeping granulomas stable?

A

CD4
If depleted, granulomas become unstable → disease

25
Q

What disease is CD4 depleted in?

A

HIV
- 20x more likely get TB
- Leading cause of death in TB

26
Q

What pro-inflammatory cytokine is also responsible for keeping granulomas stable?

A

tumour necrosis factor alpha (TNFa)
- TNF therapy, or anti-TNF for rheumatoid arthritis or organ transplant or immunocompromised can cause latent TB to cause systemic disease

27
Q

What is nucleic acid detection?

A
  • More rapid diagnosis
  • Nucleic acid amplification test using PCR
  • Sensitivity 88%, specificity 98%
  • Recommended for rapid diagnosis in TB endemic countries
28
Q

What is acid fast bacilli test?

A

stain used to identify organisms with wax-like, thick cell walls e.g.
mycobacteria (resistant to gram stain)

2a- Microbiology (14 decks)

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