Comparative evaluation of recombinant LigB protein and heat-killed antigen-based latex agglutination test with microscopic agglutination test for diagnosis of bovine leptospirosis.

This study aimed to develop latex agglutination test (LAT) using recombinant leptospiral immunoglobulin-like protein (LigB) (rLigB) antigen and compare its diagnostic efficacy with LAT using conventional heat-killed leptospiral antigen and microscopic agglutination test (MAT) in diagnosing bovine leptospirosis. The PCR-amplified 1053-bp ligB gene sequences from Leptospira borgpetersenii Hardjo serovar were cloned in pET 32 (a) vector at EcoRI and NotI sites and expressed in BL21 E. coli cells as fusion protein with thioredoxin (-57 kDa) and characterized by SDS-PAGE and immunoblot. Out of 390 serum samples [cattle (n = 214), buffaloes (n = 176)] subjected to MAT, 115 samples showed reciprocal titre≥100 up to 1600 against one or more serovars. For recombinant LigB protein/antigen-based LAT, agglutination was observed in the positive sample, while no agglutination was observed in the negative sample. Similarly, heat-killed leptospiral antigen was prepared from and used in LAT for comparison with MAT. A two-sided contingency table was used for analysis of LAT using both the antigens separately against MAT for 390 serum samples. The sensitivity, specificity and positive and negative predictive values of recombinant LigB LAT were found to be 75.65, 91.27, 78.38 and 89.96 %, respectively, and that of heat-killed antigen-based LAT were 72.17, 89.82, 74.77 and 88.53 %, respectively, in comparison with MAT. This developed test will be an alternative/complementary to the existing battery of diagnostic assays/tests for specific detection of pathogenic Leptospira infection in bovine population.