[The fundamental evaluation of COBAS TaqMan48 using clinical specimens]

When smear test is positive for acid-fast bacilli, it is important to differentiate between Mycobacterium tuberculosis complex and nontuberculosis mycobacteria (NTM) in healthcare associated infection (HAI) control. The aim of this study is to evaluate between COBAS TaqMan48 (TaqMan) and COBAS Amplicor (COBAS).

Tenfold dilution series of 5 x 10(4) cfu/mL of Mycobacterium bovis (ATCC19210) were used for evaluating the limit of detection (LOD) and reproducibility. 73 frozen clinical specimens (34 M. tuberculosis complex and 39 NTM) stored at below -20 degrees C before its use that were treated with NALC-NaOH were used to determine the agreement between two methods. Divided reaction reagents (include Master mix solution, Internal control and Mg2+) of TaqMan for 3 and 6 tests per batch used to evaluate reagents stability.

The LOD of both kits were 5 X102 cfu/mL. Regarding reproducibility, the same result was obtained when tested 3 times. The agreement rate between TaqMan and culture method was 58.8%, and between COBAS and culture method was 67.6%. When limited to smear positive eleven specimens, the agreement between TaqMan and culture method was 81.8%, and between COBAS and culture method was 90.9%. Reagents divided for 3 tests and 6 tests and stored at 4 degrees C in dark, both test reagents stability was confirmed maximum for 16 days.

As the results of the evaluation of TaqMan, the LOD, reproducibility and the agreement were similar to COBAS results. However, in low colony forming unit of clinical specimen raise the possibility that results may contain false negative.