BACTEC MGIT 960 System- Principle, Manual and Brochure

The BACTEC MGIT 960 Mycobacterial Detection System is the world's first automated system for high-volume mycobacteria growth, detection and susceptibility testing from Becton Dickinson (BD). It is non-radiometric and uses BD BBL Mycobacteria Growth Indicator Tube (MGIT) media incubated at 37°C and patented sensors, making efficient use of advanced fluorometric technology which permits highly accurate detection of O2 consumption without sharps. Automated quality control is performed continuously to ensure precise and reliable operation. Results are provided as positive/negative and numerical Growth Units . The instrument scans the MGIT every 60 minutes to detect positive tubes as indicated by an increase fluorescence.

Principle of the BACTEC MGIT 960 System 

1. MGIT Medium

The MGIT (Mycobacteria Growth Indicator Tube) consists of liquid broth medium that is known to yield better recovery and faster growth of mycobacteria. The MGIT contains 7.0  ml of modified Middlebrook 7H9 broth base. This medium is terminally sterilized by autoclaving. An enrichment, MGIT OADC (Oleic acid, Albumin, Dextrose and Catalase) or  MGIT 960 Growth Supplement, is added to make the medium complete. This Growth Supplement is essential for growth of many mycobacteria, especially those belonging to M. tuberculosis complex. Addition of the MGIT PANTA is necessary to suppress contamination. 

2. Principle of Detection and Drug Susceptibility Testing 

In addition to Middlebrook 7H9 liquid media, the MGIT tube contains an oxygen-quenched  fluorochrome, tris 4, 7-diphenyl-1, 10-phenonthroline ruthenium chloride pentahydrate,  embedded in silicone at the bottom of the tube. During bacterial growth within the tube, the  free oxygen is utilized and is replaced with carbon dioxide. With depletion of free oxygen,  the fluorochrome is no longer inhibited, resulting in fluorescence within the MGIT tube when  visualized under UV light. The intensity of fluorescence is directly proportional to the extent of oxygen depletion. MGIT tubes may be incubated at 37ºC and read manually under a UV light or entered into a MGIT 960 instrument where they are incubated and monitored for increasing fluorescence every 60 minutes. Growth of bacteria as well as mycobacteria increases the fluorescence. In case of M. tuberculosis, at the time of positivity, there are approximately 10^5- 10^6 colony forming units (CFU) per ml of medium. The instrument declares a tube negative if it remains negative for six weeks (42 days). The detection of growth can also be visually observed by the presence of a non-homogeneous light turbidity or small granular/flaky appearance in the medium. Growth of some NTM (most commonly rapid growers) results in light turbidity, while contaminating bacteria generally produce heavy turbidity. Drug susceptibility testing can be performed based on the same principle. Two MGIT tubes are inoculated with the test culture. A known concentration of a test drug is added to one of the MGIT tubes, and growth is compared with the MGIT tube without the drug (growth control). If the test drug is active against the isolated mycobacteria, it will inhibit the growth and thus there will be suppression of fluorescence, while the growth control will grow uninhibited and will have increasing fluorescence. Growth is monitored by the BACTEC

960 instrument which automatically interprets results as susceptible or resistant.

Procedure of the BACTEC MGIT 960 System (PDF)
For the detailed procedure or manual of the BACTEC MGIT 960 System, click here.

BACTEC MGIT 960 System Brochure (PDF)

To download a copy of the brochure in pdf format, click here.