ESAT-6 protein for specific Mycobacterium tuberculosis in guinea pigs skin test

Detection of Mycobacterium tuberculosis (MTB) infection by delayed-type hypersensitivity skin test with purified derivative (PPD) antigen is still used in many countries including Thailand. However, it is less specificity due to significant cross-reactivity with non-tuberculosis mycobacteria. Antigen such as early secretory antigenic target (ESAT6) is secreted in the early phase of infection and elicits cell mediated immune responses. Moreover it is found only in M. tuberculosis, M. bovis and few other mycobacterial species. ESAT-6 protein can be a good candidate for MTB specific diagnosis. Here, we report the cloning, expression, purification of ESAT-6 protein and its utility as specific antigen for MTB diagnosis by skin testing in guinea pig sensitized with killed M. tuberculosis and live BCG. Our results show that 200 mg of the purified ESAT-6 protein elicits a positive skin reactivity only in the guinea pigs sensitized with killed M. tuberculosis and not in the animals sensitized with live BCG. These data in this study support the use of ESAT-6 protein in specific detection of MTB infection.