Microbiology 17 - Mycobacterial disease

Question 1

How are mycobacteria classified?

Answer 1

Based on speed of growth
<7 days = fast
>7 days = slow

Question 2

Recall 2 examples of slow-growing mycobacteria

Answer 2

M bovis
M tuberculosis

Question 3

What is the key cell wall component of mycobacteria that makes them so different from other bacteria?

Answer 3

Long chain fatty (mycolic) acids

Question 4

Recall 2 stains that can be used to identify mycobacteria

Answer 4

Auramine - operator dependent
Ziehl Neelsen

Question 5

In which patient group is M. avium complex most common?

Answer 5

HIV positive

**resembles TB infection if underlying lung disease

Question 6

Which type of mycobacterium is associated with cardiothoracic procedures?

Answer 6

M. chimera

Question 7

Which mycobactrium species is known as the “swimming poool granuloma”?

Answer 7

M. marinum

Question 8

How can M. marinum infection present?

Answer 8

Skin lesions on hands and arms of fish-owners

Question 9

What is the main symptoms of M. ulcerans infection?

Answer 9

Painless nodules >> destructive ulceration >> scarring + contractures

causes Buruli ulcer

**buzzword- travel to australia**

Question 10

What type of infection do fast-growing mycobacteria tend to cause?

Answer 10

Skin and soft tissue infections

Question 11

How should rapid-growing mycobacteria be treated?

Answer 11

Macrolide + additional antibiotics based on susceptibility testing

Question 12

What are the two forms of leprosy?

Answer 12

1. paucibacillary leprosy - milder version
2. Multibacillary lepromatous
   - very severe
   - disseminated

Question 13

Recall some strategies for TB prevention

Answer 13

Contact tracing and treatment of index case
Screening of those considered at risk
Vaccination
Improvement of living conditions

Question 14

What is required for diagnosis of TB?

Answer 14

3 sputum samples - smear them and culture them, NAAT if possible

Question 15

What are the 2 possible tests for latent TB?

Answer 15

Mantoux test
IGRAS (detection of antigen-specific interferon gamma)

Question 16

What duration of treatment should be given in CNS TB?

Answer 16

12 months

Question 17

What is the standard treatment regimen for M. tuberculosis?

Answer 17

2/12 rifampicin, isonoazid, pyrizinamide and ethambutol

4/12 rifampicin and isoniazid

**so total 6 months

all 4 drugs for 2 months

first 2 drugs for 4 months

Question 18

What are the main side effects of each of the drugs used to treat M tuberculosis?

Answer 18

Rifampicin: orange secretions
Isoniazid: peripheral neuropathy - isoN for neuropathy. givrn with vitami b6 to prevent
Pyrizinamide: hepatotoxicity, hyperurucaemia–>gout
Ethambutol: visual disturbance - e for eyes

Question 19

How can multi-drug resistant TB be treated?

Answer 19

More than 18 months treatment with at least 5 drugs

Question 20

Where does TB infection become latent?

Answer 20

Gohn focus/ granuloma (in the lungs)

Question 21

What is the name for spinal TB?

Answer 21

Pott’s disease

Question 22

Which patients cannot receive the BCG vaccine?

Answer 22

Immunosuppressed patients as it’s a live attenuated vaccine

Question 23

What treatment is used as TB prophylaxis?

Answer 23

Isoniazid monotherapy

Question 24

Give some classical features of Leprosy

Answer 24

Skin depigmentation
Nodules
Trophic ulcers
Nerve thickening - most disability is due to nerve damage

Question 25

What is the cause of a Buruli ulcer and how does it present?

Answer 25

Mycobacterium ulcerans
Painless nodules progressing to ulceration, scarring and contractures

Question 26

Outline the outcomes of someone with TB infection exposure

Answer 26

** TB rarely causes symptoms with primary infection, only if immunocompromised

Question 27

Classic lesions of TB

Answer 27

caseating grnaulomas

Question 28

RF for TB infection

Answer 28

travel (South Asia / Eastern Europe), HIV+, homeless, IVDU, contact

Question 30

Presentation of TB in immunocompromised patient

Answer 30

• *Subacute meningitis:** headaches, personality change, meningism,
  confusion. Diagnose with LP (see meningitis section)

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

§ Milliary TB: disseminated haematogenous spread (seen on CXR)

§ Also lymphadenitis, pericarditis, peritonitis, renal, testicular, liver T

Question 31

Which area of the lung does TB affect?

Answer 31

Upper lobe- cavitation (post primary TB)

Question 32

How many sputum samples are needed to diagnose TB?

Answer 32

3

Question 33

MC&S results for TB sputum sample

Answer 33

Microscopy on Ziehl-Neelson stain;

culture on Lowenstein-Jensen medium for 6wks (gold standard) –> acid fast bacilli seen (red against blue background)

Question 34

How long does TB culture take to come back?

Answer 34

6 weeks

Question 35

Tuberculin skin test vs IGRA test

Answer 35

Tuberculin skin tests (Mantoux/Heaf): shows exposure (active/latent/ BCG)

o IGRA (Elispot/Quantiferon): shows exposure (active/latent) – NOT BCG

Question 36

What are some second line drugs for TB?

Answer 36

injectables (amikacin, kanamycin), quinolones, linezolid

Question 37

What is the risk of latent TB reactivation in an immunocompotenet individual?

Answer 37

10%

Question 38

What % of the world has latent TB infection?

Answer 38

30%

Question 39

How can leprosy present?

Answer 39

Leprosy manifests in a number of different ways due to a range of factors, most important being host immunology and bacterial virulence/initial infectious load.

At one end of the spectrum is disseminated lepromatous/ multibacillary leprosy;

Where the host immune system cannot contain the bacteria and it becomes widely disseminated

Causes peripheral nerve inflammation and damage, as well as dermatological lesions including nodules, hypoesthetic patches and the development of ‘leonine’-like facial appearance.

Nerve thickening may be felt on palpation, with the most commonly affected nerves being the ulnar, median, radial cutaneous, greater auricular, common peroneal and posterior tibial nerves.

At the other end of the spectrum is tuberculoid/paucibacillary leprosy;

Where the immune system is able to control the infection and a milder form of nerve damage and dermatological manifestations occur.

The nerve damage in all forms can lead to contractures, ulceration and deformity in the long term.

Question 40

Multi-drug resistant tuberculosis is resistant to:

Rifampicin and isoniazid

Rifampicin and ethambutol

Rifampicin and pyrazinamide

Isoniazid and ethambutol

Isoniazid and pyrazinamide

Answer 40

Rifampicin and isoniazid