Evaluation of Combined Use of BacT/ALERT 3D Liquid Culture System and PCR-RFLP for Detection and Identification of Mycobacteria from Bronchial Specimens

Background: We evaluated BacT/ALERT 3D liquid culture system (bioMeUSA) and PCR-restric- tion fragment length polymorphism (RFLP) for recov- ery and direct identification of mycobacteria, and the results were compared with a conventional culture system using an egg-based solid medium. Methods: A total of 3,037 bronchial specimens (2,309 bronchial washing fluids and 728 bronchoalveolar lavages) were collected. Decontaminated specimens were inoculated to both BacT/ALERT MP liquid me- dia and Ogawa solid media (3%, Shinyang, Korea). Recovery rate and detection time were compared be- tween the two systems. Liquid media from positive cultures were centrifuged and the pellets were tested for direct identification of mycobacteria by PCR-RFLP using Myco-ID (MD 102 isolates (28 MTB and 74 NTM) were recovered only by the liquid media, while 26 (20 MTB and 6 NTM) isolates were recovered only by the solid media. The mean time to detection was 18.1 days by the liquid media and 29.3 days by the solid media (P<0.001). The overall time to species identification from inoculation was 21.8 days. Direct PCR-RFLP from the liquid media identified 39.1% of MTB, 6.3% of M. avium, 19.05 of M. abscessus, and 12.6% of M. intracellulare respectively. Conclusion: Combined use of a liquid culture system and PCR-RFLP improved the recovery rate and shor- tened the detection time. However, solid media is still necessary to maximize the diagnostic efficiency. (Korean J Clin Microbiol 2009;12:37-42)