Comparative evaluation of the mycobacteria growth indicator tube with the BACTEC 460 TB system and Löwenstein-Jensen medium for isolation of mycobacteria from clinical specimens

Abstract

Setting: The utilization of new simples and rapid methods of diagnosis is currently of great interest for tuberculosis control.

Objective: The Mycobacteria Growth Indicator Tube (MGIT) was evaluated and compared with the BACTEC 460 TB system and Löwenstein-Jensen (LJ) medium for isolation capacity and detection time of mycobacteria.

Design: In total 337 specimens from various body sites of 276 patients were tested for the presence of mycobacteria. Specimens were decontaminated using the standard Na OH-NALC method, then processed in MGIT broth, in BACTEC vial, and on LJ medium for comparative study. Ziehl Neelsen staining was used as a reference.

Results: MGIT had 95.4% sensitivity, 100% specificity, 100% positive predictive value, and 89.3% negative predictive value. The clinical concordance between MGIT and LJ medium was 0.87 and between MGIT and BACTEC, 0.96. The mean time to detection for Mycobacterium tuberculosis was 11 days (range 7-31 days) with MGIT. For M. avium and other atypical mycobacteria, the mean time to detection were 3 and 8 days, respectively.

Conclusion: The Mycobacteria Growth Indicator Tube appears to be a rapid, easy-to-use system with a high accuracy for detecting mycobacteria directly from clinical specimens.