Comparison of the sensitivity and specificity of an automatic ligase chain reaction assay system with a one-step polymerase chain reaction assay in the diagnosis of Mycobacterium tuberculosis complex.

Background: Polymerase chain reaction (PCR) and ligase chain reaction (LCR) are two nucleic acid amplification-based molecular methods. The former has been used widely in the identification of Mycobacterium tuberculosis (M. tuberculosis). In contrast, the LCR assay which was recently introduced is not well known in our medical communities in Taiwan. To determine which method is more reliable and suitable for the identification of M. tuberculosis in our clinics, we compared the sensitivity and specificity of these two methods.

Methods: An automatic LCR assay system and a manual one-step PCR assay were studied in a side by side comparison of their performance in detection of M. tuberculosis. The automatic LCR system uses the single copy antigen protein b (Pab) gene and the manual one-step PCR assay uses the multi-copy IS6110 insertion element as the target DNA; both target DNA sequences are found specifically in M. tuberculosis complex.

Results: Both assays detected two of the M. tuberculosis complex strains, M. tuberculosis and M. bovis, but not other mycobacterial strains. In addition, both methods, which were based on different amplification principles, showed compatible sensitivity; as low as 10 and 100 copies of M. tuberculosis genomes were detected by the LCR and PCR assays, respectively. When the template DNA was less than 1000 copies, however, the automatic LCR assay system showed a lower reproducibility than that of the one-step PCR assay.

Conclusion: Our results suggest that in addition to the PCR assay, the LCR assay is a useful method for the molecular identification of M. tuberculosis complex strains.