Mycobacterium

Question 0

What is the metabolism of M.tuberculosis?

Answer 0

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

Question 1

What is the morphology of M.tuberculosis?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

1. Iron Siderophore - mycobactin.

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

Question 4

Has M.tuberculosis toxins?

Answer 4

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

Question 5

What happens in primary TB?

Answer 5

1. Asymptomatic

2. Overt disease, involving lungs or other organs.

Question 6

What happens in secondary TB?

Answer 6

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

Question 7

How do we diagnose M.tuberculosis?

Answer 7

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)

Question 8

What happens in rapid culture of M.tuberculosis?

Answer 8

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.

Question 9

What happens in PPD?

Answer 9

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

Question 10

When do we get false negatives PPD?

Answer 10

In patients with AIDS or malnourished individuals.

Question 11

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

Answer 11

1. Non motile
2. No capsule
3. No attachment pili

Question 12

What is the metabolism of M.leprae?

Answer 12

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

Question 13

What is the virulence of M.leprae?

Answer 13

1. Non motile

2. Facultative intracellular growth

Question 14

What happens in lepromatous leprosy?

Answer 14

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

Question 15

What happens in tuberculoid leprosy?

Answer 15

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.

Question 16

How do we diagnose M.leprae?

Answer 16

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).

Question 17

What is the usefulness of lepromin skin test?

Answer 17

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

Question 18

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

Answer 18

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.

Question 19

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

Answer 19

M.avium complex.

Question 20

What is the MCC of non tuberculosis mycobacterial lung disease?

Answer 20

M.avium complex.

Question 21

What are the common clinical presentations of M.kansasii?

Answer 21

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

2. Disseminated diseased in immunocompromised.

Question 22

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

Answer 22

M.kansasii

Question 23

What are the common clinical presentations of M.abscessus?

Answer 23

1. Pulmonary disease

2. Skin, soft tissue, and bone disease

Question 24

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

Answer 24

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

Question 25

What is the clinical presentation of M.fortuitum?

Answer 25

Skin, soft tissue, and bone disease.

Question 26

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

Answer 26

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

Question 27

What can M.chelonae cause?

Answer 27

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

Question 28

What is important to remember about M.chelonae?

Answer 28

Responds well to treatment.

Question 29

What can M.marinum cause?

Answer 29

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

Question 30

What is useful to remember about M.marinum?

Answer 30

Common in fresh and salt water.

Question 31

What can M.ulcerans cause?

Answer 31

"Buruli ulcers": progressive necrotic skin ulcerations.

Question 32

Where is M.ulcerans found?

Answer 32

In tropical rain forests.