Mycobacteria Growth Indicator Tube (MGIT) contains a modified Middlebrook 7H9 broth base. When supplemented with MGIT Growth Supplement and PANTA, it provides an optimum medium for the growth of a majority of mycobacterial species. All types of specimens, pulmonary as well as extra-pulmonary (except blood), can be inoculated into MGIT for primary isolation of mycobacteria.

The steps for inoculating MGIT tubes are elaborated below:

Preparation of MGIT tubes occurs after preparation of PANTA when inoculating and incubating MGIT 960 tubes for TB cultures. The preparation steps are shown below.

Preparation of PANTA is the first step when inoculating and incubating MGIT 960 tubes for TB cultures. The preparation steps are shown below (Figure 1).

Figure 1: Steps for Preparation of PANTA

Figure 2: Reconstitution of PANTA with growth supplement using a micropipette

NOTE:

Body fluids collected aseptically (cerebrospinal fluid, synovial fluid, pleural fluid) can be inoculated into MGIT medium without decontamination (with the addition of PANTA). However, since it is difficult to maintain sterile conditions throughout the collection of specimens, it is recommended that all specimens be decontaminated. 

Aseptically collected specimens need only light decontamination (NALC without NaOH). Steps for processing such specimens are:

The procedure for processing urine in TB cultures is as follows: 

• Aliquot the entire volume in several centrifuge tubes.
• Concentrate the specimen by centrifugation in 50 ml centrifuge tubes for 20-25 minutes.
• Resuspend the pellet in each tube with 1-2 ml of sterile water and pool together with a total volume of 5-10 ml.
• Decontaminate sediment with 4% sodium hydroxide (NaOH) for 15-20 minutes and proceed as similar to processing sputum.

The processed specimen is used to inoculate the MGIT tubes.

The procedure for processing tissue specimens in TB cultures is as follows:

The procedure for processing laryngeal swab specimens in TB cultures is as follows: 

The procedure for processing bronchial lavage specimens in TB cultures is the same as that for sputum samples. The following aspects need to be considered: 

• If the specimen is larger than 10 ml in volume, it needs to be concentrated by centrifugation (3000x g, 15-20 minutes) and the sediment resuspended in 5 ml sterile water.
• Thick/ mucoid samples need to be liquefied by mixing the specimen with a pinch (50-100 mg) of N-acetyl-L-cysteine (NALC) powder.

The processed specimen is used to inoculate the MGIT tubes.

Sputum specimens are viscous materials contaminated with normal flora. Therefore, processing involves pre-treatment of the sputum specimens via:​

PANTA (Figure below) is a lyophilized 5-antibiotic cocktail powder covering a broad spectrum of organisms that commonly contaminate cultures. The following are its components:

• Polymyxin B (6000 units): Works against gram-negative bacteria
• Amphotericin B (600 μg): Acts against yeast and fungi
• Nalidixic Acid (2400 μg): Works against gram negatives
• Trimethoprim (600 μg) and Azlocillin (600 μg): Works against both gram-negative and gram-positive bacteria