Potential of mycobacterial excretory secretory protein antigens (sevatb ES-31, ES-43, EST-6 and ES-20) as biomarkers to detect Mycobacterium tuberculosis bacilli.

There is a need for a simple and reliable method to identify Mycobacterium tuberculosis from nontuberculous mycobacteria (NTM). The utility of mycobacterial ES-31, ES-43, EST-6 or ES-20 antigen as a biomarker for differentiation of Mycobacterium tuberculosis bacilli from nontuberculous mycobacteria was explored using Fluorescein isothiocyanate conjugated antibodies against these antigens. Detection of these antigens was done from M.tb H(37)Ra and H(37)Rv DSS antigen. The presence of antigen in bacilli using FITC labelled antibody was indicated by green fluorescence on the cell surface while, its absence by no fluorescence under microscope. In M.tb H(37)Ra and H(37)Rv bacilli, fluorescence was observed on addition of FITC labelled anti ES-31 and anti ES-43 antibody; whereas no fluorescence was observed in case of EST-6 and ES-20 antibody conjugates. However all the antigens were detected in detergent soluble sonicate antigen of tubercle bacilli on addition of FITC conjugates. Fluorescence was not observed for ES-31, ES-43, EST-6 and ES-20 antigen in any of the tested NTM as well as in Escherichia coli. SEVA TB ES-31 and ES-43 may be used as biomarkers to distinguish M.tuberculosis bacilli from NTM.