TB and Atypical Mycobacteria

Question 1

Who discovered TB and when?

Answer 1

Dr. Robert Koch March 24th

Question 2

The close relatives of M.Tuberculosis

Answer 2

1. M.bovis (in humans and bovines)
2. M. africanum

Question 3

Explain the importance of the cell wall of M. tuberculosis

Answer 3

1. Contains long chain fatty acids and waxes that is an important virulence factor. The waxy walls allow it to survive when engulfed by macrophages
2. Structural importance: rigidity

3.Can’t be stained with normal gram staing methods and requires an acid fast stain

Question 4

Why is TB difficult to cultivate in the lab?

Answer 4

1Its slow growing with a generation time of 15-20 hrs

2. Obligate aerobe (low Os conditions)

Question 5

How is TB spread?

Answer 5

In droplets through viral shedding : coughing sneezing

Question 6

What make TB easily transmissible through the air?

Answer 6

-Droplet nuclie
-10um particle size
-stay suspended in air
-travel lower down the airway due to size

Question 7

What is the infectious dose of Tb?

Answer 7

1-10 bacilli

Question 8

Tb is contagious but not easy to acquire. What is necessary to acquire tb?

Answer 8

-Prolonged exposure
8hrs/day for up to 6 months

-Significant exposure
Crowded close communities: school, prisons, families, boarding houses

Question 9

Who are more likely to spread tb?

Answer 9

Those with a higher bioburden
-immunocompromised
-lung disease patients

Question 10

What are the steps to the prepathogenesis of tb?

Answer 10

1. Source case
2. Aerosolization
3. Airborne survival
4. Inhalation

Question 11

What are the steps for the pathogenesis of TB

Answer 11

1,Inhaled aerosols
2. Engulfed by alveolar macrophages
3 Local lymph nodes
4. Primary complex (Ghon’s focus + draining LN)
5. Initial Containment of infection
6. Latent infection
7. Heals self or Post primary tb/Reactivation

Question 12

Diagnostic test for TB in the lungs

Answer 12

1. positve TST (tb skin test) and IFN test (interferon gamma test)
2. Chest xray abnormal
3. Positive sputum smears
4. Symptoms: Cough, fever, weight loss

Question 13

What is the disadvantage of using an IFN test?

Answer 13

This would test positive for both latent and active tb and does not distinguish between

Question 14

Features of Primary Tb

Answer 14

• asymptomatic
  -Ghon’s focus/ Primary complex
  -limitted cell mediated immunity
  -Occasionally miliary
  -Erythema nodosum

Question 15

Risk factors for Reactivations

Answer 15

-Immunosuppression (HIV, chemo patients)
-Alcoholism
-Chronic illness (diabetes, chronic kidney disease)
-malnutrition
-old age

Question 16

Where can TB be located outside of the lungs?

Answer 16

Larynx
Lymph nodes
Pluera
Brain
Kidneys
Bones and joints
Genital

Question 17

Steps for the clinical approach with a probable tb case

Answer 17

1. High index of suspicions
2. Suggestive symptoms w/ a detailed history
3. Investigations
   4.Treatment
   5.Preventing onward transmission

Question 18

Symptoms of Pulmonary TB

Answer 18

Fever
Night sweats
Weight loss and anorexia
Tiredness
Cough
Breathlessness (pleural effusion)
Abnormal CXR

Question 19

What are the four types of investigations done on TB

Answer 19

1. Radiology
2. Microbiology
3. Immunology
4. Histology

Question 20

Abnormalities in a CXR when TB is suspected

Answer 20

Patchy consolidation
Cavitation usually with consolidation in the apex of the lung
Pleural effusion

Question 21

Solid media used to inoculate tn

Answer 21

LJ slopes (Lowenstien Jensen)

Question 22

Liquid Media for TB inoculation

Answer 22

MGIT: Mycobacteria Growth Indicator Tube

Question 23

Pros of LJ slants compared to MGIT liquid

Answer 23

-shorter incubation time (2-6 weeks)