Mycobacteria

Question 1

Mycobacteria are seen on gram stain?

Answer 1

No, they are not. They are slender non motile aerobic non sporing rods with a waxy coating that makes them resistant to most stains including gram stain

Once stained they are not easily decolourised (acid-fast)

Question 2

The most common mycobacteria in humans is?

Answer 2

M tuberculosis

Question 3

Following infection in a person with intact cell mediated immunity

Answer 3

Activated T cells and macrophages form granulomas that limit the spread of the organism

Question 4

Primary inoculation of the skin presents as
1.
2.

Answer 4

1. Tuberculous chancre

2. Tuberculosis verrucosa cutis

Question 5

Tuberculides are the result of immunological reactions to antigenic components of M tuberculosis usually occurring in individuals with high levels of immunity
There are 4 main forms

Answer 5

1. Lichen scrofulosorum
2. Papulonectric tuberculid
3. Erythema induratum of Bazin
4. Nodular tuberculid

Question 6

What is seen on biopsy for cutaneous TB?

Answer 6

Early stages
Acute neutrophilic inflammation with necrosis

3-6 weeks old
Granulomatous inflammation and caseation

Acid fast bacilli are present in early primary infections or in chronic lesions in those who have poor or impaired immunity.

They are not present in tuberculids

Question 7

How is TB treated?

Answer 7

Multi-drug regime to prevent resistance

Isoniazid and rifampicin are the most effective and are given in conjunction w 2 other drugs

Standard 6 month regime (RIPE)

1. Isoniazid 300mg daily
2. Rifampicin 600ng daily
3. Pyrazinamide 2g daily for the first 2 months
4. Ethambutol 15mg/kg for the first 2 months

All taken on an empty stomach

Question 8

BCG (bacillus calmette-Guerin) vaccine is an attenuated strain of M bovis

It is given to kids in endemic areas and affords protection by reducing haematogenous spread

It reduces likelihood of childhood TB by?

Answer 8

75% or more