Rapid and Simple Detection of a Mycobacterium tuberculosis Circulating Antigen in Serum Using Dot-ELISA for Field Diagnosis of Pulmonary Tuberculosis

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Abstract
Tuberculosis (TB) has re-emerged as a major health problem worldwide. Developing an easy, inexpensive immunodiagnostic test is extremely important for TB diagnosis, especially in developing countries. A target mycobacterial circulating antigen of 55-kDa molecular weight was identified in sera from confirmed Mycobacterium tuberculosis infected individuals by using Western blotting based on a specific mouse IgG anti-M. tuberculosis monoclonal antibody (TB-55 mAb). No bands were identified in sera of healthy individuals. The target TB antigen was isolated and characterized as a protein. It consists of 15 amino acids; 24.6% of the amino acids are hydrophobic and 46.4% are hydrophilic. A dot-ELISA format, based on TB-55 mAb, was developed for the direct demonstration of the 55-kDa TB antigen in serum samples of pulmonary TB patients. The technical aspects of the developed dot-ELISA are simple, rapid (5 min), and reproducible, as well as sensitive (87%) and specific (93%). Using the more sensitive immunoassay; Western blot, the 55-kDa TB antigen was detected in all (100%) sera that have been shown false negative by dot-ELISA, as well as in true positive sera. In conclusion, we have developed a simple and rapid immunoassay for the direct detection of a circulating mycobacterial antigen in sera of TB infected individuals and, therefore, the developed assay can be applied for laboratory and field diagnosis of TB infection in developing countries.

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