Diagnostic utility of a dominant outer membrane protein of Leptospira borgpetersenii Serovar Hardjo

Diagnostic ability of an immunodominant lipoprotein with a molecular weight of 32 kDa, purified from Leptospira borgpetersenii serovar hardjo, was studied. Crude outer membrane extracted from leptospiral cells were subjected to SDS-PAGE and the 32 kDa protein fraction was eluted from the excised gel. IgG fraction from sera of rabbits, hyperimmunized with the eluted 32 kDa, was used for preparing an affinity column for bulk separation of the protein in a single step. The eluted protein was strongly immunogenic in guinea pigs and its purity was established by SDS-PAGE and immunoblotting. Using ELISA, the 32 kDa protein antigen was able to detect different levels of antibodies in the sera of cattle earlier found seropositive to several Leptospira serovars using microscopic agglutination test (MAT) which is the standard serodiagnostic test. When compared with the MAT, the relative sensitivity and specificity of 32 kDa - ELISA in different serum dilutions viz., 100, 200, 400 and 800 was calculated to be 100% and 95%, 100% and 96.8%, 100% and 93.8%, and 83.33% and 100%, respectively. The study indicated that the 32 kDa protein could be used as a genus specific antigen for serodiagnosis of leptospirosis.