Mycobacterium Tuberculosis

Question 1

LABORATORY DIAGNOSIS

Question 2

Tuberculosis

Question 3

Diagnosis of active tuberculosis

Question 4

Specimen collection

Question 5

• In pulmonary TB: Sputum (2 specimens—spot and early

Question 6

morning)

Answer 6

gastric aspirate (in children)

Question 7

• In EPTB: Specimens vary depending on the site involved

Question 8

Digestion

Answer 8

decontamination and concentration of specimen:

Question 9

• Modified Petroff’s method (4% NaOH)

Question 10

• NALC (N-acetyl-L-cysteine) + 2% NaOH

Question 11

Direct microscopy by acid-fast staining:

Question 12

Ziehl-Neelsen (ZN) technique-long slender

Answer 12

beaded

Question 13

uniformly stained red color acid-fast bacilli

Question 14

• Kinyoun’s cold acid-fast staining

Question 15

• Fluorescent (auramine) staining—it is more sensitive and

Question 16

smears can be screened more rapidly than ZN stain

Question 17

Conventional culture media-take 6-8 weeks

Question 18

• Lowenstein Jensen (L) medium-shows rough

Answer 18

tough and

Question 19

buff colored colonies in 6-8 weeks

Question 20

Automated culture methods-take 3-4 weeks

Question 21

• MGIT system: Detects growth as well as resistance to

Question 22

antitubercular drugs (ATDs)

Question 23

Culture identification

Question 24

• Automated identification—by MALDI-TOF

Question 25

• MPT 64 antigen detection—by ICT

Question 26

Molecular methods

Question 27

• PCR detecting IS6110 gene

Question 28

• CBNAAT (GeneXpert) and Truenat—for identification and

Question 29

detection of resistance to rifampicin; has a turnaround time

Question 30

2 hours

Question 31

• Line probe assay (e.g. Genotype TB)-for identification

Question 32

and detection of resistance to 1st and 2nd line ATDs; has a

Question 33

turnaround time of 2-3 days.

Question 34

Diagnosis of latent tuberculosis

Question 35

By tuberculin skin test (e.g. Mantoux test) and interferon gamma

Question 36

release assay (IGRA).