A mycobacterial excretory-secretory
protein fraction ESAS-7 purified by 50%
ammonium sulphate precipitation followed by SDS-PAGE fractionation was evaluated by
penicillinase enzyme linked immuno-sorbent assay (ELISA) for its sensitivity and specificity in the diagnosis of
pulmonary tuberculosis. At a "cut off" serum dilution of 600, 38 (90%) of 42 sera from bacteriologically confirmed
tuberculosis cases, 15 (100%) of 15 sera from bacteriogically negative but anti tubercular
therapy (ATT) responded cases, 3 (7%) of 43 sera from normal healthy subjects and 4 (8%) of 48 sera from non tuberculous disease control cases gave positive reaction for tubercular antibody to ESAS-7
antigen fraction containing predominantly 33-kDa
protein with a sensitivity of 90% in bacteriologically confirmed cases and specificity of 92%. Further, this diagnostic assay using the ESAS-7
antigen is more sensitive requiring as little as one nanogram
antigen per test compared to use of 100 nanogram EST-6
antigen reported earlier. Thus use of ESAS-7
antigen for antibody detection has good diagnostic potential with improved specificity in
pulmonary tuberculosis.