B-cell epitope mapping of the VapA protein of Rhodococcus equi: Implications for early detection of R-equi disease in foals

Linear B-cell epitopes of the Rhodococcus equi virulence-associated protein (VapA) were mapped using a synthetic peptide bank in this study. The pepti des were screened in an enzyme-linked immunosorbent assay (ELISA) with a to tal of 70 sera from foals with current R. Equi disease (51 sera), as well a s from foals that had either recovered from R. equi infection 10 months pre viously (3 sera) or that had no known history of R. equi disease (16 sera). An epitope with the sequence NLQKDEPNGRA was identified and was universall y recognized by all 51 sera from foals with R. Equi disease and was not rec ognized by any of the other sera. There was poor reactivity between all ser a and peptides relating to other areas of the VapA protein. It is proposed that an ELISA based upon a defined peptide epitope may be used in an improv ed serological diagnostic test for R. Equi infection in foals.