MGIT DST Quality Control

MGIT DST Quality Control

Quality control of MGIT DST is critical to laboratory testing, as it ensures the accuracy and consistency of the test processes and the results reported. 

Frequency: 

It is important to perform quality control (QC) of drug susceptibility testing periodically. This testing must be performed:

• For each new batch of reagents (MGIT drug kits, other drugs, media, etc.) 

•  Weekly, in a DST run, when patient tests are run weekly.

• With each batch of patient isolates, when DST is performed less frequently.

• If the batch QC fails, all the results obtained within that batch and the new batch of a reagent should be thoroughly reviewed, and the testing should be repeated.

Strains used of MGIT DST Quality control: 

• M. tuberculosis H₃₇Rv (ATCC [American Type Culture Collection] number 27294) is used as a QC strain which is susceptible to all anti-tuberculosis drugs. If the ATCC reference strain cannot be obtained, a well-characterized strain derived from a patient’s isolate that is completely susceptible to first-line anti-TB agents may be used instead. It is preferable to use a strain that has been fully sequenced and shown to have a wild-type pattern for all known genes associated with TB drug resistance.

• It is not necessary to include a resistant strain, as most of the resistant strains against a drug which are available from ATCC and other culture collections are highly resistant and do not give any added benefit in quality control.

Procedure: 

The test procedure for QC organisms is the same as for clinical isolates. The inoculum should be from a freshly grown culture in the MGIT medium or on the Löwenstein-Jensen medium (LJ) slant. After a standardized suspension has been made, it should be frozen at -70° C ±10° C. It may be stored for up to 1 year with no significant decrease in viable counts.

Resources

1. 1. STANDARD OPERATING PROCEDURE FOR MYCOBACTERIOLOGY LABORATORY

2. Revised National TB Control Programme Training Manual for Mycobacterium tuberculosis Culture & Drug susceptibility testing. Central TB Division, Ministry of Health and Family Welfare, GOI. 

3. Technical manual for drug susceptibility testing of medicines used in the treatment of tuberculosis. World Health Organization 2018.

Assessment