Use of ESAT-6-CFP-10 fusion protein in the bovine interferon-gamma ELISPOT assay for diagnosis of Mycobacterium bovis infection in cattle.

Bovine tuberculosis (BTB) is a chronic bacterial disease, and a major animal health problem with zoonotic implications. Screening of mycobacterial infections in bovines is traditionally done using the single intradermal tuberculin test. Though the test is widely used, it has its own disadvantages and they include its inability to distinguish between pathogenic and non-pathogenic mycobacterial infections owing to its low specificity. Furthermore, the associated operative difficulties of this test have driven the quest for discovery of new antigens and diagnostic assays leading to the development of the interferon (IFN)- test. Presently, combinatorial testing using the skin test and the interferon gamma assays are being used in the diagnosis of BTB in various control and surveillance programs. In this study, we report the cloning, expression and purification of ESAT-6-CFP-10 fusion protein and its further use in the development of the IFN- gamma ELISPOT assay for accurate diagnosis of BTB in cattle. The BTB diagnosis employing the ELISPOT assay was evaluated using peripheral blood mononuclear cells from culture positive and culture negative cattle. The ELISPOT assay showed higher specificity and sensitivity in detecting BTB when a recombinant ESAT-6-CFP-10 fusion protein was used. The present study indicated that the usefulness of the fusion protein can replace the ESAT-6, CFP-10 or combination of both proteins for detecting BTB in IFN-gamma ELISPOT assay.