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3. Read SK medium up to 6 weeks
4. MTB appears as whitish granular or flaky growth that settles down at the
bottom
5. If the SK medium shows growth or contamination (in the form of turbidity)
and inoculate deposit on LJ medium alone and read up to 8 weeks
6. Even if the SK medium shows no growth within 6 weeks, proceed with
LJ medium alone and read up to 8 weeks
7. If LJ shows typical MTB growth within 8 weeks, report immediately after
confirmation
8. Report as negative only after LJ completes 8 weeks (a total of 14 weeks)
6. Processing of extra pulmonary samples for MGIT960
Isolation of M. tuberculosis by MGIT system requires the final inoculum to be in
an ideal condition that will not interfere with the fluorescence.
6.1 Pus and other muco-purulent specimens
1. Thick pus of volume >10 ml is decontaminated using the NALC NaOH
method as sputum
2. If the volume is < 10 ml, either aliquot and process only 10 ml by NALC
NaOH method or concentrate the initial volume by centrifugation for 15 20
minutes and resuspend the pellet in 5 ml of sterile distilled water. If the pus is
too thick, add about 50-100 mg of NALC powder; mix well and
decontaminate using NaOH. Resuspend the final pellet in buffer to reduce the
pH
3. If the pus is not thick, decontaminate using 2-4% NaOH. The concentration of
NaOH can be changed based on the expected level of contamination in the
specimen which depends on the site of collection
6.2 Gastric aspirates
1. Distribute the volume in smaller aliquots and centrifuge the tubes at 3000 x g
2. Pool the deposits, add 5ml distilled water and decontaminate it using NALC-
NaOH or 2-4% NaOH
6.3 Bronchial washings
1. Process using NALC-NaOH like sputum
2. If the specimen is >10 ml in volume, process the whole specimen.
3. If <10ml, concentrate the specimen by centrifugation (3000x g, 15-20
minutes)
4. Add 5 ml sterile water to the pellet and decontaminate as for sputum
6.4 Laryngeal swabs
1. Transfer the swab into a sterile centrifuge tube and add 2 ml sterile water.
2. Add 2 ml of NaOH-NALC solution and mix well in a vortex mixer.
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