Mycobacterium Tuberculosis

Question 1

Mycobacteria classification

Answer 1

M.tuberculosis
M.leprae
M.bovis
Atypical mycobacterium

Question 2

Mycoside of m.tuberculosis

Answer 2

Trehalose dimycolate (virulence factor)

Question 3

Transmission

Answer 3

Respiratory aerosol
M.bovis (ingestion of cow’s milk, causes git tb)

Question 4

Initial site of infection

Answer 4

Lungs

Question 5

Types of lesions

Answer 5

1) Exudative- acute inflammatory response at initial site of infection in lung
2) Granulomatous- central area of caseating necrosis surrounded by epitheloid cells, giant cells and macrophages

Question 6

Test for tb

Answer 6

PPD: intradermal injection of antigenic protein particles from killed m.tuberculosis results in localised skin swelling and redness in infected person

Question 7

Alternative to PPD skin tests

Answer 7

IGRAS (interferon-gamma release assays)

Question 8

False positive ppd test

Answer 8

Due to BCG vaccine which is effective in preventing severe forms of tb in children, but it provides minimal immunity in later years

Question 9

Chest xray of an infected person

Answer 9

Granuloma, ghon complex, ghon focus or old scarring in the upper lobes

Question 10

MDR tuberculosis

Answer 10

Multi-drug resistant tb (resistant to isoniazid and rifampin)

Question 11

XDR tuberculosis

Answer 11

Extremely drug resistant tb (resistant to isoniazid, rifampin, a flouroquinolone and an injectable agent like aminoglycoside)

Question 12

Treatment of MDR & XDR tb

Answer 12

Use of multiple second-line agents for an extended period of time (18-24mo)