Exam 3 (Mycobacteria)

Question 1

Mycobacteria:
Gram:
Stain:
Preferred growth medium:
O2 req:

Answer 1

Gram: G+
Stain: acid-fast or fluorescence
Growth: facultative intracellular (macrophages)
O2 req: obligate aerobe (lung macrophages)

Question 2

What is the main reservoir for mycobacterium and how are they spread? How many cells for infection?

Answer 2

• humans
• airborne transmission
• little as 10 cells

Question 3

The _________________ step of acid fast staining drives the red dye into cells with _________ in their cell membranes.

Answer 3

• hot carbol fuscin

- mycolic acid

Question 4

What is cord factor? What cells is it found on? What kind of molecule is it?

Answer 4

A glyco-lipid found on mycobacterium that is associated with mycolic acid. Assists in cell-cell adhesion and helps with “cord-like” growth of these cells.

Question 5

_________ and __________ facilitate the slow ________ growth in mycobacterium that strongly correlates with virulence.

Answer 5

• Cord-factor
• mycolic acid
• cord-like

Question 6

What is unique about immune responses to mycobacterium? What immune cells are involved?

Answer 6

• virulence of M. tuberculosis and M. leprae trigger immune response that causes the disease.
• CD4+ T-cells and macrophages

Question 7

How do mycobacterium survive in macrophages?

Answer 7

inhibition of phago-lysosome fusion

Question 8

What are the two characteristics of a tubercle caused by TB?

Answer 8

• granuloma surrounded by punctate nuclei of lung tissue and inflammatory leukocytes
• centra area of necrosis where nuclei have been destroyed

Question 9

T or F:

Once a pt is asymptomatic with TB, they are considered cured.

Answer 9

FALSE

-life-long disease, once infected can be asymptomatic but never cured

Question 10

What age group has a high risk of developing progressive TB?

Answer 10

children under 5 years

Question 11

Outcomes of untreated TB:

• ___% no disease
• ___% clinical TB
• ___% progressive systemic disease and death

Answer 11

• 91% no disease
• 6% clinical TB (2 pulm, 3 extrathoracic, 1 both)
• 3% progressive sys dis and death

Question 12

What form of TB is most contagious? What causes it?

Answer 12

• Secondary Tuberculosis

- caused by endogenous reactivation of prior infection stimulated by stress, malnutrition, and HIV

Question 13

What is a Mantoux Reaction? What triggers it?

Answer 13

• positive tuberculin test
• triggered by subdermal PPD (processed protein derivative of cell wall of M. tuberculosis)

+: >10mm redness
strong+: >20mm redness

Question 14

What is BCG and why is is not used in the US?

Answer 14

Bacille Calmette-Guerin is derivative of M. bovis. Used for vaccination against TB.
-discouraged in US because it gives positive TB test and is infectious in immunocompromised pts

Question 15

What is isoniazid?

Answer 15

effective chemotherapeutic agent against TB

Question 16

What are the three main CMI outcomes of M. leprae?

Answer 16

1. HEALTHY: Effective CMI = healthy
2. TUBERCULOID: TH1-response = macrophages kill nerves, macules and plaques without sensation
3. LEPROMATOUS: bag prognosis for recovery, highly infectious

Question 17

What happens in a TH2 response to TB?

Answer 17

-cytotoxic T-cell lysis and loss of tissue including nerves

Question 18

What multidrug therapy is effective against Leprosy?

Answer 18

Dapsone + Rifampin + Clofazimine (rising resistance is becoming a problem)

Question 19

All pathogenic mycobacterial species have ____________.

Answer 19

slow growth rates

Question 20

Difference in clinical features and Tx of M. tuberculosis vs M. leprae?

Answer 20

TB-
Clinical features: pulmonary and extrapulmonary tb
Tx: multidrug therapy for 6-12 months

Leprosy-
Clinical features: tuberculoid-to-lepramatous leprosy
Tx: multidrug therapy for 2+ years

Question 21

Epidemiology of M. tuberculosis?

Answer 21

• aerosol
• all ages
• highest risk to immune compromised

Question 22

Epidemiology of M. leprae?

Answer 22

-close physical contact

Question 23

Gram type of Nocardia?

Answer 23

G+ (poor staining)

Question 24

What is notable about the staining technique needed for Nocardia?

Answer 24

mycolic acid in cell wall allows for acid-fast staining to differentiate from fungal look-alikes

Question 25

Nocardia is an ________________ for _________ patients.

Answer 25

• opportunistic

- immunocompromised