Comparison of a nonradiometric liquid-medium method (MB REDOX) with the BACTEC system for growth and identification of mycobacteria in clinical specimens

Early identification of tuberculosis in the clinical setting is of great importance in order for specific therapy to be swiftly initiated. MB REDOX (Heipha Diagnostika), a growth-based medium without radioactive materials, was evaluated and was compared to the BACTEC system for detection of mycobacteria, including the Mycobacterium tuberculosis complex and atypical mycobacteria. MB REDOX consists of a Kirchner medium enriched with growth- promoting additives, antibiotic compounds, and a redox indicator which can be monitored to detect growth of mycobacteria with the naked eye. MB REDOX only detects growth and cannot differentiate the M. tuberculosis complex (M. tuberculosis, M. bovis, and M. africanum) from other species of Mycobacterium. Therefore, PCR-restriction fragment length polymorphism analysis (PRA) was used in this investigation to identify to the species level organisms showing positive growth with MB REDOX. Our data demonstrate the usefulness of MB REDOX for the detection of mycobacteria in clinical specimens. The rate of detection of M. tuberculosis complex with MB REDOX (84.3%) was higher than that with the BACTEC system (68.6%). When combined with PRA for species identification, MB REDOX is easy to perform and is suited to most clinical laboratory settings for the detection and identification of mycobacteria.