Mycobacteria growth indicator tube

"MGIT" redirects here. For other uses, see MGIT (disambiguation).

Mycobacteria Growth Indicator Tube (MGIT) is intended for the detection and recovery of mycobacteria. The MGIT Mycobacteria Growth Indicator Tube contains 7 mL of modified Middlebrook 7H9 Broth base. The complete medium, with OADC enrichment and PANTA antibiotic mixture, is one of the most commonly used liquid media for the cultivation of mycobacteria.

All types of clinical specimens, pulmonary as well as extra-pulmonary (except blood and urine), can be processed for primary isolation in the MGIT tube using conventional methods. After processed specimen is inoculated, MGIT tube must be continuously monitored either manually or by automated BACTEC MGIT 960 System until positive or the end of the testing protocol.

Principles of the Procedure

A fluorescent compound is embedded in silicone on the bottom of 16 x 100 mm round bottom tubes. The fluorescent compound is sensitive to the presence of oxygen dissolved in the broth. Initially, the large amount of dissolved oxygen quenches emissions from the compound and little fluorescence can be detected. Later, actively respiring microorganisms consume the oxygen and allow the fluorescence to be detected.

Tubes entered into the BACTEC MGIT 960 System are continuously incubated at 37°C and monitored every 60 minutes for increasing fluorescence. Analysis of the fluorescence is used to determine if the tube is instrument positive; i.e., the test sample contains viable organisms. An instrument-positive tube contains approximately 105 to 106 colony-forming units per milliliter (CFU/mL). Culture tubes which remain negative for a minimum of 42 days (up to 56 days) and which show no visible signs of positivity are removed from the instrument as negatives and sterilized prior to discarding.

Alternatively inoculated tubes could be read daily by using Wood's lamp or other long-wave UV light source.