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, nonradiomet ric 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 pr ocessed specimens were inoculated into all media in parallel. Specimens inc luded 383 respiratory samples, 20 urine samples, 23 purulent exudates, 13 s tool samples, 103 blood samples, 14 bone marrow aspirates, and 44 body flui d 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 numb er 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 c ontamination 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 w ith other liquid culture methods, MB/BacT should be used in combination wit h a solid medium, not on its own.