Evaluation of a commercial radiometric system for primary isolation of mycobacteria over a fifteen-year period.

The rate of recovery and time to detection of mycobacteria from clinical specimens were analysed for specimens inoculated into both radiometric Middlebrook 7H12 (Bactec 12B, originally 12A) medium and Lowenstein-Jensen egg-based medium (with and without sodium pyruvate) over the 15-year period from 1980 to 1994. A total of 19,679 Bactec vials were inoculated together with Lowenstein-Jensen slopes, with 2198 mycobacterial isolates detected. The mean times to detection for Bactec and Lowenstein-Jensen were 11.7 days and 23.9 days, respectively. In 195 cases mycobacteria were isolated from Bactec and not from Lowenstein-Jensen, whereas the reverse was true in 42 cases. The number of contaminated Bactec vials was 488 and the number of contaminated Lowenstein-Jensen slopes 448.