Detection of Mycobacterium tuberculosis complex Using Real-time Polymerase Chain Reaction / 대한진단검사의학회지

BACKGROUND: For the detection of Mycobacterium tuberculosis complex (MTB), PCR is known to be sensitive, specific, and rapid compared to the conventional methods of acid-fast-bacilli (AFB) smear and culture. We evaluated a new approach for MTB detection using real-time PCR. METHODS: The specificity of real-time PCR was evaluated using 20 MTB isolates and 37 nontuberculous mycobacteria (NTM) isolates identified by AccuProbe Mycobacterium tuberculosis complex colony identification test (Gen-Probe Inc., USA) and Myco-ID (M&D, Korea). One hundred sputum specimens (50 AFB smear-positive and 50 negative specimens) were analyzed using real-time PCR and Amplicor Mycobacterium tuberculosis test (Roche, Germany). The results of real-time PCR positives (55 samples) and negatives (598 samples) were analyzed by AFB smear and culture. RESULTS: The real-time PCR assay accurately discriminated between MTB and NTM species. Realtime PCR and Amplicor test yielded the same results in 96.0% (96/100) of the sputum specimens tested. The sensitivity and specificity of real-time PCR based on AFB culture were 97.4% and 88.5%, respectively. Of the 55 real-time PCR positive specimens, 83.6% (46/55) were culture-positive, 30.9% (17/55) were smear-positive, 52.7% (29/55) were smear-negative and culture-positive, and 14.5% (8/55) were both smear and culture-negative. Among the 598 real-time PCR negative specimens, 60 were not tested for AFB smear or culture and 10 were contaminated. Of the remaining 528 specimens, 478 (90.5%) were both smear and culture-negative and 39 (7.4%) were culture-positive. CONCLUSIONS: For the detection of MTB, real-time PCR was sensitive and specific and comparable to conventional methods. It can be used for rapid identification of M. tuberculosis in clinical laboratories.

Usefulness of Multiplex Real-Time PCR and Melting Curve Analysis in Identification of Nontuberculous Mycobacteria / 대한진단검사의학회지

BACKGROUND: Nontuberculous mycobacteria (NTM) should be correctly identified to the species level, because of different treatment plans among NTM species. This study was performed to assess the usefulness of real-time PCR and melting curve analysis in the identification of NTM. METHODS: One hundred fifty-two clinical NTM isolates were identified to the species level by PCR-restriction fragment length polymorphism analysis (PRA). Those strains were then identified by multiplex real-time PCR and melting curve analysis on the 16S rRNA gene and hsp65 gene. RESULTS: In the 16S rRNA gene fragment analysis, M. abscessus-M. chelonae group showed melting point at temperatures above 65 degrees C and M. avium complex (MAC; M. avium and M. intracelluare) below 48 degrees C, which differentiated M. abscessus-M. chelonae group and MAC from other NTM. In the hsp65 gene fragment analysis, M. abscessus-M. chelonae group was clearly divided into M. abscessus type I, M. abscessus type II, and M. chelonae according to the melting points at 61.25 degrees C, 66.06 degrees C, and 57.58 degrees C, respectively. CONCLUSIONS: With the multiplex real-time PCR and melting curve analysis of 16S rRNA and hsp65 genes, M. abscessus and M. chelonae were readily identified and MAC were differentiated from other NTM. Especially, M. abscessus and M. chelonae, which were not differentiated from each other with the 16S rRNA gene fragment analysis, were identified with hsp65 gene fragment analysis.