Mycobacterium – TB Susceptibility Testing
|Test Requested||Required Requisition(s)||Specimen Type||Minimum Volume||Collection Kit|
Mycobacterium – TB Susceptibility testing
M. tuberculosis complex culture
Submission and Collection Notes
Submit viable growth of a viable M. tuberculosis complex culture on solid or in liquid Mycobacterium culture medium.
Contaminated or non-viable cultures will not be tested.
Preparation Prior to Transport
Label the specimen container with the patient’s full name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.
Place specimen container in the biohazard bag and seal bag, and insert the completed requisition in the pocket on the outside of the sealed biohazard bag.
Continue to incubate if transport is delayed more than one hour. Specimens should be transferred to the lab ASAP where possible.
Test Frequency and Turnaround Time (TAT)
Mycobacterium tuberculosis complex susceptibility testing is performed daily from Monday to Friday.
Turnaround time for 1st line MTBC susceptibility testing is up to 12 days from the date of the culture report.
Turnaround time for reporting 2nd line MTBC susceptibility results is up to 12 days after the 1st line test results are reported.
Results are reported to the ordering physician or health care provider as indicated on the requisition.
Specimens that are positive for Mycobacterium tuberculosis complex are reported to the Medical Officer of Health as per Health Protection and Promotion Act.
Susceptibility testing for MTBC is performed using the BACTEC MGIT 960 method, Becton Dickinson, MD. For information on the BACTEC 960 see BACTEC MGIT 960 User’s manual.
The first culture of MTBC isolated from a patient is routinely tested for susceptibility to each of the four first line anti- tuberculosis drugs isoniazid (INH), rifampin (RIF), ethambutol (EMB) and pyrazinamide (PZA). Susceptibility testing to the first line drugs is repeated at three months if cultures are still positive.
MTBC isolates resistant to INH at 0.1mg/L are also tested at 0.4 mg/L and Moxifloxacin and is also tested. Any test that shows resistance to rifampin or any two of the first line drugs is further tested for susceptibility to second line drugs.
In the case of resistance to PZA, testing to determine whether the strain is M.bovis or M.bovis BCG is automatically performed at the TB and Mycobacteriology Laboratory in Toronto since these species are resistant to PZA.