Development of a Quantitative Sandwich Enzyme-Linked Immunosorbent Assay for Detecting the MPT64 Antigen of Mycobacterium tuberculosis

PURPOSE: Tuberculosis (TB) is a major infectious disease and is responsible for two million deaths annually. For the identification and quantitation of Mycobacterium tuberculosis (M. tuberculosis), a causative agent of TB, a sandwich enzyme-linked immunosorbent assay (ELISA) against the MPT64 protein of M. tuberculosis, an antigen marker of the M. tuberculosis complex, was developed. MATERIALS AND METHODS: The MPT64 protein was expressed, and anti-MPT64 monoclonal antibodies were prepared. A sandwich ELISA was established using recombinant MPT64 protein and anti-MPT64 monoclonal antibodies. The sandwich MPT64 ELISA was evaluated using reference and clinical mycobacterial strains. RESULTS: The sandwich MPT64 ELISA detected MPT64 protein from 2.1 ng/mL to 250 ng/mL (equivalent to 1.7×10(4) CFU/mL and 2.0×10(6) CFU/mL). All 389 clinical M. tuberculosis isolates tested positive in the sandwich MPT64 ELISA (sensitivity, 100%), and the assay showed no cross reactivity to any tested nontuberculous mycobacterial strain (specificity, 100%). CONCLUSION: The sandwich MPT64 ELISA is a highly sensitive and quantitative test for MPT64 protein, which can identify M. tuberculosis.