Development and evaluation of a multiplex loop-mediated isothermal amplification (LAMP) assay for differentiation of Mycobacterium tuberculosis and non-tuberculosis mycobacterium in clinical samples.

INTRODUCTION

The rapid and accurate diagnosis of tuberculosis (TB) is important to reduce morbidity and mortality rates and risk of transmission. Therefore, molecular detection methods such as a real-time PCR-based assay for Mycobacterium tuberculosis (MTB) have been commonly used for diagnosis of TB. Loop-mediated isothermal amplification (LAMP) assay was believed to be a simple, quick, and cost-effective isothermal nucleic acid amplification diagnostic test for infectious diseases. In this study, we designed an in-house multiplex LAMP assay for the differential detection of MTB and non-tuberculosis mycobacterium (NTM), and evaluated the assay using clinical samples.

MATERIAL AND METHODS

For the multiplex LAMP assay, two sets of specific primers were designed: the first one was specific for IS6110 genes of MTB, and the second one was universal for rpoB genes of mycobacterium species including NTM. MTB was confirmed with a positive reaction with both primer sets, and NTM was identified with a positive reaction by only the second primer set without a MTB-specific reaction. Total 333 clinical samples were analyzed to evaluate the multiplex LAMP assay. Clinical samples were composed of 195 positive samples (72 MTB and 123NTM) and 138 negative samples. All samples were confirmed positivity or negativity by real-time PCR for MTB and NTM. Analytical sensitivity and specificity were evaluated for the multiplex LAMP assay in comparison with acid fast bacilli staining and the culture method.

RESULTS

Of 123 NTM samples, 121 were identified as NTM and 72/72 MTB were identified as MTB by the multiplex LAMP assay. False negative reactions were seen only in two NTM positive samples with co-infection of Candida spp. All 138 negative samples were identified as negative for MTB and NTM. Analytical sensitivity of the multiplex LAMP assay was 100% (72/72) for MTB, and 98.4% (121/123) for NTM. And the specificity of assay was 100% (138/138) for all.

CONCLUSIONS

Our newly designed multiplex LAMP assay for MTB and NTM showed relatively good sensitivity in comparison with previously published data to detect isolated MTB. This multiplex LAMP assay is expected to become a useful tool for detecting and differentiating MTB from NTM rapidly at an acceptable sensitivity.