Isolation ofMycobacterium Tuberculosis 31 kDa antigen protein of diagnostic interest from culture filtrate using anti-ES-31 antibody by affinity chromatography.

Proteins secreted into the culture medium byMycobacterium tuberculosis (M. tb) are shown to be source of antigens of immunodiagnostic interest. Anin vitro released 31 kDa antigen ESAS-7F isolated fromM.tb H(37)Ra culture filtrate by salt precipitation, SDS-PAGE and cation exchange fast protein liquid chromatography (FPLC) was shown earlier to be a diagnostically important antigen fraction. In this report, we describe the isolation of ESAS-7F antigen using monospecific antibody coupled to sepharose CL-4B column. The percentage recovery of ESAS-7F antigen using affinity chromatography was approximately 8% of the total ES antigen proteins compared to 0.05% obtained by conventional purification steps using salt precipitation, SDS-PAGE and FPLC. Similar seroreactivity was observed by the antigen isolated by both the methods in indirect ELISA. Affinity chromatography helped in an increased recovery of ESAS-7F antigen and obviates the need for time consuming conventional purification steps.