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Year 2 > Mycobacteria > Flashcards

Mycobacteria Flashcards

1
Q

What species causes Tuberculosis

A

M. tuberculosis

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2
Q

What species causes Chronic lung infection

A

MAC

M. Kansasii

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3
Q

What species causes fish tank granuloma

A

M. Marinum

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4
Q

What species causes Buruli ulcer

A

M. ulcerans

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5
Q

What species causes leprosy

A

M. leprae

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6
Q

Are mycobacteria aerobic or anaerobic

A

Aerobic

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7
Q

Can mycobacteria be destained by acid and alcohol

A

No

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8
Q

Shape of mycobacteria

A

bacillus

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9
Q

Define bacillus

A

Rod-shaped, Gram-positive and aerobic

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10
Q

Where are mycobacteria found

A

Inside macrophages

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11
Q

Relative growth rate of mycobacteria

A

Slow REPRODUCTION
Slow GROWTH in Human
Slow GROWTH IN CULTURE
Slow RESPONSE TO TREATMENT

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12
Q

4 aspects of Koch’s postulates

A
  1. Bacteria should be found in all people with disease
  2. Bacteria should be isolated from the infected lesions in people with the disease
  3. Pure culture inoculated in a person should show symptoms of the disease
  4. Same bacteria should be isolated from the intentionally infected individual
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13
Q

Why are mycobacteria resistant to gram-stain

A

High lipid content with mycelia acids in the cell wall causing them to become v-shaped

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14
Q

What stain is needed for acid fast bacilli

A

Ziehl-Neelsen stain (AFB)

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15
Q

What are the three elements of the Ziehl-Neelsen stain

A
  1. Carbol fuchsin
  2. Acid Alcohol
  3. Methylene Blue
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16
Q

How much AFB is needed per ml sputum

A

10,000 AFB

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17
Q

Difference between Fluorochrome stains and AFB stain

A

Fluorochrome stains aid screening at lower power objective lenses

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18
Q

What colour does the Ziehl-Neelsen stain give when the test is positive for acid-fast bacilli

A

Red/Pink

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19
Q

How do we analyse nucleic acid of mycobacterium

A

PCR

Produces rapid results

20
Q

What bacteria is PCR used for diagnosis and why

A

TB

Fast and specific

21
Q

How do mycobacteria cause disease

A
  1. Acid fast bacilli are phagocytose and placed in phagolysosome
  2. Bacteria adapts to intracellular environment and withstands phagolysosomal killing
  3. Escapes to cytosol
  4. Host tries to kill mycobacterium via microbicidal molecules
  5. These assist in digestion and degradation by bacterial proteases
  6. Degraded into antigens for T cell presentations

Ignored by immune system

22
Q

Describe the normal immunological process that take place following invasion of a pathogen

A
  1. CD4 cells produce INF-gamma

2. IL-12 further stimulates the release of INF gamma

23
Q

What are granulomas

A

Lesions that arise in response to containing mycobacteria

24
Q

How does mycobacteria granulomas form

A
  1. Macrophages become epithelioid cells
  2. Macrophages fuse together to form giant multinucleate cells
  3. T cells infiltrate the granuloma
  4. Central tissues necrose to form caveating granuloma
  5. Granuloma prevents nutrients from entering - starving the mycobacteria forming cavities
25
Q

Why is a granuloma dangerous for a bacteria and how is this overcome by mycobacteria

A
  1. Nutrients can’t enter the granuloma

2. Mycobacteria goes into dormant state (TB) until conditions are better

26
Q

Role of CD8 cells

A

Lyse infected macrophages

27
Q

Why would we get a disorganised granuloma

A
  1. TNF neutralisation causes cells within the granuloma to no longer be as tightly clustered
28
Q

In what individuals is TB activation with a greater risk

A
  1. Age
  2. Malnutrition
  3. Intensity of exposure
  4. Immunosuppression
29
Q

Why does M. tuberculosis cause activation of the immune system

A

Lipid-rich cell wall stimulates T-cell response 3-9 weeks after exposure

30
Q

Positive effects of immunological stimulation from TB

A
  1. Macrophages kill mycobacteria
  2. Containment of infection
  3. Granuloma
31
Q

Negative effects of immunological stimulation from TB

A
  1. Hypersensitivity Type 4
  2. Skin lesions
  3. Eye lesions
  4. Swelling of joints
32
Q

How can immunological reactivity to TB be measured

A

Tuberculin skin test

INF gamma release assays

33
Q

Describe the tuberculin skin test

A
  1. Intradermal injection of purified protein derivatives induce skin swelling and redness
34
Q

What is Tuberculoid leprosy

A
  1. Associated with type 4 hypersensitivity and granulomata
  2. Paucibaccillary lesions with low mycobacteria no.
  3. Tissue damage
  4. Involves Th1 CD4 cells and IFN-gamma and TNF-alpha
35
Q

What is the lepromatous leprosy

A
  1. Lesions full of bacilli but no granulomata
  2. Skin lesions
  3. Predominant Th2 biased CD4 T-cell responses with IL-4,5,10 production
36
Q

What are the three categories of leprosy

A
  1. Tuberculoid
  2. Lepromatous
  3. Borderline
37
Q

Tuberculoid vs Lepromatous leprosy

A

Tuberculoid - immune response is good and only few lesions + mildly contagious
Lepromatous - Immune response poor + affects skin, nerves organs + widespread lesions + more contagious

38
Q

Where do bacilli settle in primary TB

A
  1. Apex of the lungs
39
Q

How are bacilli removed from apex in primary TB

A

Lymphatics to hilar lymph nodes

40
Q

Why do bacilli settle at the apex in primary TB

A
  1. More air and less blood supply thus few defending white cells
41
Q

What is the primary complex

A

Granuloma
Lymphatics
Lymph Nodes

42
Q

Why is caseous material coughed out from the lung in pulmonary TB

A
  1. Cell-mediated immunity and necrosis = abscess of bacilli which is coughed up
43
Q

Can TB spread beyond the lung

A

Yes:
Pleura
Bones
Genito-urinary tract

44
Q

What is latent TB

A
  1. Cell mediated response from T-cells

2. Primary infection is contained but cell-mediated immunity persists

45
Q

What can be seen on an X-ray in an individual with latent TB

A

Normal chest

46
Q

How can we detect Latent TB

A

Tuberculin skin test

47
Q

When does pulmonary TB take place

A

Following primary TB

Year 2 (155 decks)

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