460 TB System, and Löwenstein-Jensen Medium

Using two different liquid media and one conventional solid medium, a total of 57 mycobacterial isolates (Mycobacterium tuberculosis, n 5 55; nontuberculous mycobacteria, n 5 2) were recovered from 377 clinical specimens. The rates of recovery of M. tuberculosis were 96.4 % with the BACTEC MGIT 960 liquid medium, 92.7 % with BACTEC 12B liquid medium, and 81.8 % with the Löwenstein-Jensen (LJ) medium. The mean time to detection of M. tuberculosis in smear-positive specimens was 12.6 days for BACTEC MGIT 960 medium, 13.8 days for BACTEC 12B medium, and 20.1 days for LJ medium, and in smear-negative specimens it was 15.8 days for BACTEC MGIT 960 medium, 17.7 days for BACTEC 12B medium, and 42.2 days for LJ medium. The rates of contamination were 3.7, 2.9, and 1.2 % for the BACTEC MGIT 960, BACTEC 12B, and LJ media, respectively. In conclusion, the nonradiometric, fully automated 7-ml BACTEC MGIT 960 system can be considered a viable alternative to the semiautomated, radiometric BACTEC 460 TB system. The use of the radiometric BACTEC 460 TB broth-based system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) considerably improves the recovery of and de-creases the time required to detect mycobacteria; however, this procedure is still labor-intensive and requires attention to spe-cial safety and regulatory issues regarding radioisotopes (7). Previous reports have demonstrated that the 4-ml Mycobacte