Method Description

This test method is based on presence or absence of growth of Mycobacterium tuberculosis complex in broth cultures with the presence of critical concentrations of the antimycobacterial drugs isoniazid, rifampin, and ethambutol. One of 2 FDA-cleared platforms (VersaTREK or BD MGIT 960) may be used.

The VersaTrek platform uses the presence or absence of a pressure increase inside broth vials containing M tuberculosis complex in the presence of critical concentrations of the antimycobacterial drugs isoniazid, rifampin, and ethambutol. Increasing pressure indicates the presence of actively growing M tuberculosis that is resistant to the critical concentration of drug contained in the broth. Low or undetectable pressure increases in the presence of critical drug concentrations suggests a lack of M tuberculosis complex growth and susceptibility to the drug at the tested concentration. Antimycobacterial drugs and concentrations tested are: isoniazid (0.1 mcg/mL and 0.4 mcg/mL), rifampin (1 mcg/mL), and ethambutol (5 mcg/mL and 8 mcg/mL).(Package insert: VersaTREK Mycobacteria Detection and Susceptibility Testing system, TREK Diagnostics, 10/2018)

The BACTEC MGIT 960 platform uses the production and measurement of fluorescence within a mycobacterial growth indicator tube (MGIT) in the presence of actively growing M tuberculosis complex isolates in the presence of critical concentrations of the antimycobacterial drugs isoniazid, rifampin, and ethambutol. Low or undetectable levels of fluorescence in the presence of critical drug concentrations suggest lack of M tuberculosis growth and susceptibility to the drug tested at the tested concentration. Increased fluorescence suggests active growth of M tuberculosis and resistance to the drug at the tested concentration. Antimycobacterial drugs and concentrations tested are: isoniazid (0.1 mcg/mL and 0.4 mcg/mL), rifampin (2 mcg/mL), and ethambutol (5 mcg/mL).(Package insert: BACTEC MGIT 960 SIRE Kit, BD Diagnostics, 10/2016)