Clinical evaluation of a loop-mediated isothermal amplification (LAMP) assay for detecting Mycobacterium tuberculosis in sputum

Abstract

ABSTRACT

Tuberculosis (TB) is an infectious disease that is caused by M. tuberculosis complex and still remained one of the leading causes of death from infectious diseases in the world. Culture confirmation of Mycobacterium tuberculosis takes at least six weeks and other diagnostic methods often give false results, therefore, new diagnostic technique should be developed to control tuberculosis disease effectively. A sensitive and efficient loop-mediated isothermal amplification (LAMP) assay targeting hspX was established for diagnosis of M. tuberculosis more rapidly and accurately in this study. TB hspX LAMP assay condition was optimized at 67oC for 60 min. TB hspX LAMP primers are only specific to M. tuberculosis since the LAMP reaction showed positive results only with M. tuberculosis and negative results with the other bacterial strains tested. The detection limit of TB hspX LAMP and TB hspX PCR was 10 and 10,000 copies per reaction, respectively, implying the sensitivity of TB hspX LAMP was 1,000 times better than that of TB hspX PCR. For the clinical evaluation, culture confirmation, PCR, and LAMP assay were applied to 303 sputum specimens. PCR assay targeting hspX showed no positive results among the sputum specimens. Therefore, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of TB hspX LAMP were calculated 71.1%, 98.8%, 91.4% and 95.1%, respectively in comparison with TB culture as the gold standard for diagnosis of M. tuberculosis. The LAMP method validated in this study could be applied to the clinical specimens for detection of M. tuberculosis and could be used as diagnosis for TB patients on their hospital visit.