ELISA analysis of BACTEC bottles for the earlier diagnosis of tuberculosis

Enzyme-linked immunosorbent assays (ELISA) have enabled earlier identification of Mycobacterium tuberculosis (TB) in clinical settings by utilizing both TB antibody and antigen detection. We studied the sensitivity and specificity of ELISA detection of TB antigen by using a commercially available anti-BCG antibody in conjunction with BACTEC 7H12B culture bottles. We compared these results against those obtained with cultures of Mycobacterium avium-intracellulare and Mycobacterium kansasii. All BACTEC bottles were inoculated with known concentrations of organisms. TB antigen was detected by ELISA in BACTEC culture bottles of TB 12 days before the BACTEC system could itself identify the species. A growth index of greater than or equal to 10 reliably indicated that tuberculosis antigen was detectable by ELISA. The correlation between growth index and antigen concentration was extremely high (r = 0.95 and p less than 0.001). There was insignificant cross-reactivity with the other atypical mycobacteria at the levels of growth tested. This technique potentially offers a sensitive and specific means for the early identification of TB in BACTEC culture bottles.