Improved detection and differentiation of mycobacteria with combination of Mycobacterium Growth Indicator Tube and Roche COBAS AMPLICOR System in conjunction with Duplex PCR.

In this study, a combination of liquid and solid media (current "gold standard" for culture) with combinations of liquid media (Mycobacteria Growth Indicator Tube (MGIT)) plus a commercial amplification system (Roche COBAS AMPLICOR System (CAS)), and solid media (Ogawa) plus CAS for detection of Mycobacterium tuberculosis were compared. In addition, the ability of the MGIT to recover mycobacteria from various clinical samples was compared with the abilities of egg-based Ogawa medium using equal volume of samples and a high concentration (6%) of NaOH for decontamination. A total of 705 specimens (395 respiratory and 310 extrapulmonary) that were collected from 554 patients were tested in parallel with three assays. The results of MGIT and Ogawa were evaluated with the "gold standard" (combination of culture and clinical data) and those of CAS were evaluated with extended gold standard including treated tuberculosis. A total of 130 mycobacterial infections (M. tuberculosis, n=122; mycobacterium other than tuberculosis (MOTT), n=8) were detected. The differentiation of M. tuberculosis and MOTT was successfully accomplished using duplex PCR. The overall sensitivity of the MGIT, Ogawa, and CAS for M. tuberculosis was 89.9%, 73.9%, and 79.9%, respectively. For the MOTT, the corresponding values for the MGIT and Ogawa medium were 100% and 12.5%, respectively. The mean detection time for M. tuberculosis was 22 days using MGIT and 32 days when using the Ogawa medium. The specificity of CAS was 98.4%, with an inhibition rate of 1.4%. A combination of MGIT plus CAS detected 97.5% of all M. tuberculosis infections (compared with MGIT plus Ogawa, 91.8%, P<0.05; compared with Ogawa plus CAS, 87.7%. P<0.01). Our results indicate that a combination of MGIT plus a Roche CAS in conjunction with duplex PCR, would be quite useful in clinical laboratories for both rapid detection and differentiation of M. tuberculosis and MOTT.