Mycobacteria Growth Indicator Tube (MGIT) is intended for the culture, detection and recovery of

mycobacteria ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis ('' M. tuberculosis'') and ...

. The MGIT Mycobacteria Growth Indicator Tube contains 7 mL of modified

Middlebrook 7H9 Broth Middlebrook 7H9 broth is a liquid growth medium specially used for culture of'' Mycobacterium'' species, notably '' Mycobacterium tuberculosis''. Composition * Ammonium sulfate * L-Glutamic acid * Sodium citrate * Pyridoxine * Biotin * Disodium ph ...

base. The complete medium, with OADC enrichment and PANTA

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

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 Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...

and

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

), 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

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

compound is embedded in

silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...

on the bottom of 16 × 100 mm round bottom tubes. The fluorescent compound is sensitive to the presence of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

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

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s 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 the BD BACTEC microMGIT fluorescence reader or a

Wood's lamp A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a separat ...

or other long-wave

UV light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

source.

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. Its usefulness has been evaluated in the scientific literature."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

References

{{Tuberculosis, state=collapsed Bacteriology Tuberculosis