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Revival of the frozen cultures 

The MGIT system automatically and continuously incubates and monitors tubes once they are placed in a station; there is no need to remove the tubes from the instrument. 

Cultures during incubation:

1. Cultures remain in their stations until signalled “positive”, or if no growth is detected after 42 days incubation, are signalled “negative”. 

2. If an instrument-positive tube is determined to be smear-negative for either mycobacteria or contaminants, the tube may be re-entered into the instrument, but within 5 hours of removal.

A sterility check of growth is ascertained to differentiate M. tuberculosis from other contaminants in MGIT-positive tubes. 

BHI (Brain Heart Infusion) Agar plates are used for sterility checks using the following steps:

1. Divide the plate into 4 quadrants so that four specimens can be subcultured onto one plate. 

2. Label the plate with specimen ID

   Steps to Preserve and Store MTB Cultures 

Quality control (QC) Testing of 7H9 Liquid Medium

Every new lot of MGIT medium and every new lot of the enrichment should be quality control tested by the user upon receipt and before it is used routinely.

A. QC strains

Cultures: The following three mycobacterial cultures are recommended for quality control testing.

1.M. tuberculosis, H37Rv ATCC 27294
2.M. kansasii ATCC 12478
3.M. fortuitum ATCC 6841

Liquid media are used in the mycobacteriology laboratory for sub-culturing stock strains for storing strains at - 80°C and other in-vitro tests.

 MTB isolates from all positive cultures (using the LJ subculture from an

Maintenance and Storage of Mycobacterial Strains