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Test ID: CTB    
Mycobacterial Culture

Method Description Describes how the test is performed and provides a method-specific reference

The BBL MGIT Mycobacteria Growth Indicator Tube contains 7 mL of modified Middlebrook 7H9 broth base.(5,6) The complete medium, with OADC Enrichment and PANTA Antimicrobic Mixture, is 1 of the most commonly used liquid media for the cultivation of mycobacteria.

 

The BACTEC MGIT 960 System is designed for the rapid detection of mycobacteria in clinical specimens. The system includes a liquid culture medium (BBL MGIT Mycobacteria Growth Indicator Tube), a growth supplement (BBL MGIT OADC Enrichment) and an antibiotic mixture (BBL MGIT PANTA). BBL MGIT OADC Enrichment provides substances essential for the growth of mycobacteria. BBL MGIT PANTA contains a mixture of antimicrobial agents used to suppress the growth of contaminating bacteria.

 

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

 

The automated BACTEC MGIT 960 System monitors the tubes hourly for increasing fluorescence. Analysis of the fluorescence is used to determine if the tube is instrument-positive; ie, the test contains viable organisms. 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.(Youmans GP: Cultivation of mycobacteria, the morphology and metabolism of mycobacteria. In Tuberculosis. Edited by GP Youmans, Philadelphia, WB Saunders Company, 1979, pp 25-35; Kent PT, Kubica GP: Public health mycobacteriology: a guide for the level III laboratory. USDHHS, CDC, Atlanta, 1985)

Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.

Monday through Sunday; Continuously

Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.

60 days/Positive cultures reported as soon as detected, Negative 60 days

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

70 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

Raw specimen 2-14 days; Positive cultures kept 1 year.

Performing Laboratory Location The location of the laboratory that performs the test

Rochester