4. TB - Tuberculosis

Question 1

What is Tuberculosis (TB)?

Answer 1

An infectious disease caused by the mycobacterium tuberculosis bacteria.

Question 2

Describe the staining features of TB.

Answer 2

1. Acid-fast bacilii
   - Are resistant to the acids used in the staining procedure. This property is called acid-fastness.
2. Stain red/pink against a blue background with Z-N stain
   - Require a special staining technique using the Zeihl-Neelsen stain.
   - This turns TB bacteria bright red against a blue background.

Question 3

Why does TB not react well to gram staining?

Answer 3

Ineffective gram staining:
-> Only stained weakly with Gram stain due to waxy cell wall coating composed of high lipid content.

Question 4

Describe the appearance of TB.

Answer 4

Aerobic, non-motile, non-sporing, slightly curved rods/bacilli (ROD-SHAPED) with a thick waxy capsule.

Question 5

What are the 4 main species that can cause TB?

Answer 5

Caused by 4 main mycobacterial species:

1. Mycobacterium tuberculosis - most common cause
2. Mycobacterium bovis - where milk is unpasteurised
3. Mycobacterium africanum
4. Mycobacterium microti

Question 6

What is the most common cause of TB?

Answer 6

Mycobacterium tuberculosis

Question 7

Is TB fast or slow growing?

Answer 7

Slow growing - generation time is 15-20 hours.

Question 8

Give some risk factors for TB.

Answer 8

Immunocompromised states:
1. HIV+
2. Diabetes Mellitus
3. Malnutrition
4. Ageing
5. Chronic lung disease (esp. silicosis)
6. Immunosuppressant medications

Substance abuse:
6. IVDU
7. Alcoholics

8. Close contact with active TB infection
   - Healthcare workers
   - Prisons
9. Origination from a high-incidence country
   e.g. Sub-saharan Africa

Question 9

How is TB spread?

Answer 9

An airborne infection spread via respiratory droplets.