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Microbiology > Mycobacterium > Flashcards

Mycobacterium Flashcards

0
Q

What is the metabolism of M.tuberculosis?

A
  1. Aerobic
  2. Catalase (+)
  3. Slow growth rate
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1
Q

What is the morphology of M.tuberculosis?

A
  1. 40% of total cell dry weight is lipid.
  2. Composed of mycolic acids.
  3. Thin rods.
  4. Non motile.
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2
Q

What is the role of mycosides in the virulence of M.tuberculosis?

A
  1. Cord factor
  2. Sulfatides - inhibit phagosome-lysosome fusion.
  3. Wax D - acts as an adjuvant
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3
Q

Besides mycosides, what other virulent factors does M.tuberculosis utilize?

A
  1. Iron Siderophore - mycobactin.

2. Facultative intracellular growth - Can survive and multiply in macrophages.

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4
Q

Has M.tuberculosis toxins?

A

Neither exotoxin nor endotoxins. It has lipopolysaccharide, but no lipid A.

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5
Q

What happens in primary TB?

A
  1. Asymptomatic

2. Overt disease, involving lungs or other organs.

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6
Q

What happens in secondary TB?

A
  1. Pulmonary problems
  2. Pleural or pericardial lesions
  3. Lymph node infection
  4. Kidney
  5. Skeletal
  6. Joints
  7. CNS
  8. Miliary TB
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7
Q

How do we diagnose M.tuberculosis?

A
  1. Acid-fast stain of specimen.
  2. Rapid culture
  3. PPD skin test
  4. IGRA (interferon gamma release assay)
  5. Chest X ray
  6. Gene Xpert MTB/RIF (and similar PCR based studies)
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8
Q

What happens in rapid culture of M.tuberculosis?

A
  1. Bactec radio metric culture, a liquid broth in a bottle, with radioactive palmitate as a carbon source.
  2. Mycobacteria grow and use carbon, allowing early detection (1-2 weeks), even before colonies can be seen.
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9
Q

What happens in PPD?

A

Measure of zone of induration:
>5mm: immunocompromised host.
>10mm: chronic disease or risk factors for exposure to TB.
>15mm: all others.

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10
Q

When do we get false negatives PPD?

A

In patients with AIDS or malnourished individuals.

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11
Q

What is useful to remember about the virulence of M.tuberculosis?

A
  1. Non motile
  2. No capsule
  3. No attachment pili
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12
Q

What is the metabolism of M.leprae?

A
  1. Catalase (+)
  2. Grows best at low temperatures
  3. Phenolase (+) - converts dopa into pigmented product (used for diagnosis).
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13
Q

What is the virulence of M.leprae?

A
  1. Non motile

2. Facultative intracellular growth

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14
Q

What happens in lepromatous leprosy?

A
  1. Low cell-mediated immunity
  2. Organisms found everywhere (organs and blood)
  3. Skin, nerves, eyes and testes involved bilaterally.
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15
Q

What happens in tuberculoid leprosy?

A
  1. Intact cell-mediated immunity
  2. Difficult to isolate M.leprae from skin or blood.
  3. Skin and nerves involved: 1-2 unilateral superficial lesions.
16
Q

How do we diagnose M.leprae?

A
  1. Can not be grown on artificial media. Only be cultured in certain animals, such as mice foot, pads, armadillos, or monkeys.
  2. Skin or nerve biopsies - will reveal acid-fast bacilli (lepromatous) or granulomas (tuberculoid).
17
Q

What is the usefulness of lepromin skin test?

A

Not in diagnosis, but in positioning of patients on the immunologic spectrum.

18
Q

What are the common clinical presentations of M.avium complex?

A
  1. In AIDS patients –> disseminated infection with fever, weight loss, diarrhea, hepatitis.
  2. In immunocompetent host –>
    a. Upper lung cavitary disease in elderly smokers.
    b. Middle and lower lung nodular and bronchiectatic disease in middle-aged female non-smokers.
  3. Lymphadenitis –> in children.
19
Q

What should you suspect when you see fever of unknown origin in AIDS patients?

A

M.avium complex.

20
Q

What is the MCC of non tuberculosis mycobacterial lung disease?

A

M.avium complex.

21
Q

What are the common clinical presentations of M.kansasii?

A
  1. Pulmonary: upper lung cavitary disease (resembles TB).

2. Disseminated diseased in immunocompromised.

22
Q

What is the 2nd MCC of non tuberculosis mycobacterium lung disease in the US?

A

M.kansasii

23
Q

What are the common clinical presentations of M.abscessus?

A
  1. Pulmonary disease

2. Skin, soft tissue, and bone disease

24
Q

What is useful to keep in mind about M.abscessus?

A

Rapid grower: usually grows in culture in <7 days.

25
Q

What is the clinical presentation of M.fortuitum?

A

Skin, soft tissue, and bone disease.

26
Q

What is useful to keep in mind about M.fortuitum?

A
  1. Rapid grower
  2. Common lab contaminant
  3. Associated with contaminated foot baths
27
Q

What can M.chelonae cause?

A
  1. Skin, soft tissue, and bone disease.
  2. Disseminated disease (immunocompromised)
  3. Keratitis - associated with contact use
28
Q

What is important to remember about M.chelonae?

A

Responds well to treatment.

29
Q

What can M.marinum cause?

A

Skin, soft tissue, and bone disease (Fish tank granuloma).

30
Q

What is useful to remember about M.marinum?

A

Common in fresh and salt water.

31
Q

What can M.ulcerans cause?

A

“Buruli ulcers”: progressive necrotic skin ulcerations.

32
Q

Where is M.ulcerans found?

A

In tropical rain forests.

Microbiology (46 decks)

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