Comparison of a nonradiometric system with Bactec 12B and culture on egg-based media for recovery of mycobacteria from clinical specimens

The MB/BacT (Organon-Teknika, USA) is a fully automated, rapid, nonradiometric system for the culture of mycobacteria from clinical samples. The rate of recovery of mycobacteria and the time to detection obtained with the MB/BacT were compared with those obtained with Lowenstein-Jensen and Coletsos solid media and Bactec 7H12 (12B) (Becton-Dickinson, USA) broth when 600 processed specimens were inoculated into all media in parallel. Specimens included 383 respiratory samples, 20 urine samples, 23 purulent exudates, 13 stool samples, 103 blood samples, 14 bone marrow aspirates, and 44 body fluid samples or aspirates. Overall, 106 mycobacterial isolates comprising six species were recovered, of which 100 (94.3%) were detected with MB/BacT, 98 (92.5%) with egg-based media, and 96 (90.2%) with Bactec 12B. The recovery rates of Mycobacterium tuberculosis complex with MB/BacT, egg-based media, and Bactec 12B were 98.7%, 93.7, and 89.9%, respectively. The average number of days to detection of single mycobacterial isolates was 14.2 days for MB/BacT, 26.1 days for egg-based media, and 11.7 days for Bactec 12B. The contamination rates were higher in MB/BacT (5%) than in Bactec 12B (1.8%) or egg-based media (1.5%). MB/BacT is a reliable, nonradiometric, less labor-intensive alternative to Bactec 12B for recovery of mycobacteria, but, as with other liquid culture methods, MB/BacT should be used in combination with a solid medium, not on its own.