KatG protein: A novel marker for differential diagnosis of Myobacterium avium   complex infection

Purpose: Biochemical or nucleic acid based diagnostic techniques for MAC infection are unsatisfactory. This study aims to identify and evaluate M. avium secretory protein(s) of diagnostic potential, so as to develop a rapid and simple method for diagnosis of MAC infection.
Material and Methods:Initially, a specific protein band of ~80-85 kDa was recognised by differential immunoblotting; which was subjected to anion exchange column chromatography for purification of proteins. After fractionisation using SDS-PAGE and electroelution, blast search was carried out. Further immunoreactivity studies were done with M. avium and Mtb infected mice sera. Clinical utilisation of separated protein was evaluated by conducting indirect ELISA with serum samples from mycobacterial infected patients.
Results: A specific 81.6 kDa protein, shown to be catalase-peroxidase protein (KatG) by blast search was separated. Immunoreactivity studies of purified KatG proteins with mice sera confirmed it to be specific for M. avium infection. Indirect ELISA with patient samples further confirmed it to be M. avium infection specific.
Conclusion: KatG protein is specifically recognised by MAC patients and can be used as a marker for simple and rapid ELISA based tests for differential diagnosis of M. avium infection.

Keywords
Differential diagnosis, enzyme linked immunosorbent assay, mycobacterium avium infection, secretory proteins