Mycobacteria growth indicator tube

Mycobacteria Growth Indicator Tube (MGIT) is intended for the detection and recovery of mycobacteria. The MGIT Mycobacteria Growth Indicator Tube contains 4 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 instruments 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 × 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 are filled with samples in the broth and continuously incubated at 37°C. The tubes are monitored for increasing fluorescence to determine if the tube is instrument positive; i.e., the test sample contains viable organisms. Fluorescence can be recorded by automated instruments such as Becton Dickinson's BACTEC MGIT 960 System, or manually using Wood's lamp or other long-wave UV light source.[1]

Instruments

BACTEC MGIT 960 System

This instrument is produced by Becton Dickinson (BD). It is specially designed to accommodate Mycobacteria Growth Indicator Tube (MGIT) and incubate them at 37°C. The instrument scans the MGIT every 60 minutes for increased 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 discarded.[2] Its usefulness has been evaluated in the scientific literature.[3][4][5]

References

  1. ↑ Siddiqi, Salman H.; Sabine Rüsch-Gerdes (2006). Procedure Manual For BACTEC MGIT 960 TB System.
  2. ↑ Siddiqi, Salman H.; Sabine Rüsch-Gerdes (2006). Procedure Manual For BACTEC MGIT 960 TB System.
  3. ↑ "Use of BACTEC MGIT 960 for Recovery of Mycobacteria from Clinical Specimens: Multicenter Study" Enrico Tortoli, Paola Cichero, Claudio Piersimoni, M. Tullia Simonetti, Giampietro Gesu, and Domenico Nista Journal of Clinical Microbiology, November 1999, p. 3578-3582, Vol. 37, No. 11
  4. ↑ "Evaluation of Automated BACTEC MGIT 960 System for Testing Susceptibility of Mycobacterium tuberculosis to Four Major Antituberculous Drugs: Comparison with the Radiometric BACTEC 460TB Method and the Agar Plate Method of Proportion" Enrico Tortoli, Marta Benedetti, Alessandra Fontanelli, and M. Tullia Simonetti Journal of Clinical Microbiology, February 2002, p. 607-610, Vol. 40, No. 2 doi:10.1128/JCM.40.2.607-610.2002
  5. ↑ "Evaluation of the fully automated Bactec MGIT 960 system for the susceptibility testing of Mycobacterium tuberculosis to first-line drugs: a multicenter study" Fanourios Kontosa, Maria Maniatia, Christos Costopoulosb, Zoe Gittic, Stavroula Nicolaoub, Efymia Petinakia, Spyridoula Anagnostoub, Ioannis Tselentisc and Antonios N. Maniatis Journal of Microbiological Methods Volume 56, Issue 2, February 2004, Pages 291–294 doi:10.1016/j.mimet.2003.10.015
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