CTB - Performance: Mycobacteria and Nocardia Culture

Test Catalog

Test Name

Test ID: CTB    
Mycobacteria and Nocardia Culture

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

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 (growing) 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 that remain negative for a minimum of 42 days and that show no visible signs of positivity are removed from the instrument as negatives.


In addition to the MGIT tube, Middlebrook 7H10/7H10S agar biplates are inoculated and incubated at 37 degrees C. Growth from positive MGIT tubes or agar plates is identified using a variety of techniques including Hologic/GenProbe AccuProbes, MALDI-TOF mass spectrometry, or 16S rRNA gene sequencing. The Mycobacterium tuberculosis complex will be identified to the species level upon request, using rapid PCR.(Pfyffer GE, Palicova F: Mycobacterium: general characteristics; laboratory detection, and staining procedures. In Manual of Clinical Microbiology. 10th edition. Vol 1, Edited by J Versalovic, KC Carroll, G Funke, et al. Washington, DC: ASM Press. 2011 pp 472-502; Halse TA, Escuyer VE, Musser KA: Evaluation of a single tube multiplex real-time PCR for differentiation of the Mycobacterium tuberculosis complex in clinical specimens. J Clin Microbiol 2011 Jul;49[7]:2562-2567 doi: 10.1128/JCM.00467-11)

PDF Report Indicates whether the report includes an additional document with charts, images or other enriched information


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.

62 days/Positive cultures reported as soon as detected, Negative 62 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 3-7 days; Isolates from positive cultures kept 1 year.

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