MI: Mycobacterial Diseases Pt.1

Question 1

How can mycobacteria be categorised?

Answer 1

Rapid-growing and slow-growing

Question 2

List three types of mycobacterial complex.

Answer 2

Mycobacterium tuberculosis complex

• Mycobacterium tuberculosis
• Mycobacterium bovis

Mycobacterium avium complex

• Mycobacterium avium
• Mycobacterium intracellulare

Mycobacterium abscessus complex

• Mycobacterium abscessus
• Mycobacterium massiliense
• Mycobacterium bolletii

Question 3

Describe the morphology of mycobacteria.

Answer 3

• Non-motile rod-shaped bacteria
• Relatively slow-growing
• Cell wall composed of mycolic acids, complex waxes and glycoproteins
• Acid-alcohol fast

Question 4

What is used as a screening test for mycobacterial infections?

Answer 4

Auramine stain

Question 5

How are non-tuberculous mycobacterial infections transmitted?

Answer 5

• NOT person-to-person
• From the environment
• May be colonising rather than infecting

Question 6

List three examples of slow-growing non-tuberculous mycobacteria and the diseases that they cause.

Answer 6

Mycobacterium avium intracellulare

• May invade bronchial tree or pre-existing bronchiectasis/cavaties
• Disseminated infection in immunocompromised patients

Mycobacterium marinum

• Swimming pool granuloma

Mycobacterium ulcerans

• Skin lesions (e.g. Bairnsdale ulcer, Buruli ulcer)
• Chronic progressive painless ulcer

Question 7

List three examples of rapid-growing non-tuberculous mycobacteria.

Answer 7

• Mycobacterium abscessus
• Mycobacterium chelonae
• Mycobacterium fortuitum

Question 8

List some risk factors for NTM.

Answer 8

Age

Underlying lung disease

Question 9

How is Mycobacterium avium intracellulare treated?

Answer 9

• Clarthromycin/azithromycin
• Rifampicin
• Ethambutol
• +/- streptomycin/amikacin

Question 10

What are the two types of Mycobacterium leprae infection?

Answer 10

• Paucibacillary tuberculoid - few skin lesions (usually <5), robust T cell response, low number of bacteria in the body
• Multibacillary lepromatous - multiple skin lesions (usually >5), poor T cell response, high number of bacteria

Question 11

What is the most common cause of death by infectious agent in the world?

Answer 11

• 1 = HIV
• 2 = TB (10% of world infected)

Question 12

How many species are part of the Mycobacterium tuberculosis complex?

Answer 12

7 (including Mycobacterium tuberculosis, bovix and africanum)

Question 13

What is the generation time of Mycobacterium tuberculosis?

Answer 13

15-20 hours

Question 14

What is the infectious dose of Mycobacterium tuberculosis?

Answer 14

1-10 bacilli

Question 15

What are the 2 types of primary TB infection

Answer 15

• Latent TB
  
  • Asymptomatic
  • Not contagious
• Active primary TB
  
  • Symptomatic
  • Infectious
  • Can cause progessive disseminated disease

Question 16

What is post-primary (secondary) TB?

Answer 16

Reactivation or exogenous re-infection

10% chance after primary infection

Question 17

List some risk factors for reactivation of TB.

Answer 17

• Immunosuppression
• Chronic alcohol excess
• Malnutrition
• Ageing

Question 18

List some types of extra-pulmonary TB.

Answer 18

• Lymphadenitis (scrofula) - cervical lymph nodes most commonly
• Gastrointestinal - due to swallowing of tubercle
• Peritoneal - ascitic or adhesive
• Genitourinary
• Bone and joint - due to haematogenous spread (e.g. Pott’s disease)
• Miliary TB
• Tuberculous meningitis

Question 19

Why is it important to take 3 sputum samples when investigating suspected TB?

Answer 19

Increases the sensitivity of the smear microscopy

Question 20

What is the turnaround time for smear microscopy and PCR?

Answer 20

2 hours