Micro 13: Mycobacterial Diseases

Question 1

Describe the different possibilities that can occur when you get exposed to TB?

Answer 1

Exposure to TB -> Infection or non-infection

If infected, can cause primary TB -> this is basically when you have symptoms
If infected, usually becomes latent (no symptoms) -> infection multiplies at pleural surface in Ghon focus, but controlled in caseating granuloma (basically a collection of macrophages)

Latent TB -> no reactivation (no symptoms) or can cause reactivation / Post-primary TB (symptoms)

Question 2

What are the symptoms of TB seperated by systems?

Answer 2

General: Fever, night sweats, weight loss, ethnicity/travel

Pulmonary: Cough, haemoptysis

Meningitis: Subacute headache, personality change, meningism, confusion

Spinal (Pott’s disease): Back pain, discitis, vertebral destruction, iliopsoas abscess

Miliary: Disseminated haematogenous

Question 3

What can usually trigger reactivation in latent TB?

Answer 3

Latent TB may be latent forever, or can be activated (so you get symptoms)

Reactivation happens with immunosuppression, illness etc.

Question 4

What are mycobacteria on gram stain?

Answer 4

Gram +ve aerobic RODS

Question 5

What are the Ix required for TB?

Answer 5

CXR - Upper lobe cavitation

3x sputum sample - as TB is hard to grow:

• Microscopy using Ziehl-Neelson stain
• Cultured on Lowenstein-Jensen medium 6w (GS)
• Which will reveal Acid-fast bacilli

Exposure:

• Tuberculin skin test (mantoux / heaf) - shows previous exposure = active/latent/BCG
• IGRA (Interferon Gamma Release Assay / Elispot) = Active/ Latent -> NOT BCG

Question 6

What is the mx for TB?

Answer 6

RIPE:

Rifampicin - 6/12
Isoniazid - 6/12
Pyrazinamide - 2/12
Ethambutal - 2/12

NB: Resistance is becoming problematic – 2nd line treatment includes injectables (amikacin), linezolid

Question 7

What is Leprosy caused by?

Answer 7

Mycobacteria leprae

Question 8

What are the features of leprosy infections?

Answer 8

Skin pigmentation

Nodules

Nerve thickening -> neurological symptoms

Question 9

What are the features of mycobacterium Avium-Intracellulare complex?

Answer 9

Disseminated infection in immunocompromised

Question 10

What are the features of Mycobacterium Marinarum?

Answer 10

Fish tank granuloma ->

Aquarium owners

Question 11

What are the features of Mycobacterium ulcerans?

Answer 11

Buruli ulcer ->

Australia; ulcerating nodules

Question 12

Which TB investigation may be positive in somebody who has had the BCG vaccine?

a) Sputum cultures
b) Blood cultures
c) Tuberculin skin test
d) IGRA
e) CXR

Answer 12

c) Tuberculin skin test

Question 13

Which stain is used to visualise TB on microscopy?

a) Gram stain
b) Methylene blue
c) Lowenstein-Jensen
d) Ziehl-Neelson 
e) Tuberculin

Answer 13

d) Ziehl-Neelson

Question 14

List some side-effects of:​

Rifampicin ​

Isoniazid ​

Pyrazinamide ​

Ethambutol ​

Answer 14

Rifampicin ​- orange secretions​

Isoniazid ​- peripheral neuropathy (B6 deficiency)

Pyrazinamide ​- hepatotoxic, hyperuricaemia

Ethambutol ​- optic neuritis (pain, vision loss, one eye)​

Question 15

What is an auramine stain useful for?

Answer 15

acid-fast bacilli

Question 16

What are the two types of Mycobacterium leprae infection and their features?

Answer 16

Paucibacillary tuberculoid​

• few skin lesions​
• hairless plaques​
• loss of sensation​
• robust T cell response​

Multibacillary lepromatous ​

• multiple skin lesions​
• poor T cell response​
• Thickened dermis​
• Lion like face​