Molecular characterization, occurrence, and immunogenicity in infected sheep and cattle of two minor outer membrane proteins of Brucella abortus.

Screening of a Brucella abortus genomic library with two sets of monoclonal antibodies allowed the isolation of the genes corresponding to two minor outer membrane proteins (OMP10 and OMP19) found in this bacterial species. Sequence analysis of the omp10 gene revealed an open reading frame capable of encoding a protein of 126 amino acids. The nucleotide sequence of the insert producing the OMP19 protein contains two overlapping open reading frames, the largest of which (177 codons) was shown to encode the protein of interest. Analysis of the N-terminal sequences of both putative proteins revealed features of a bacterial signal peptide, and homology to the bacterial lipoprotein processing sequence was also observed. Immunoblotting with monoclonal antibodies specific for OMP10 or OMP19 showed that both proteins are present in the 34 Brucella strains tested, representing all six Brucella species and all their biovars. The OMP19 detected in the five Brucella ovis strains examined migrated at an apparent molecular weight that is slightly higher than those of the other Brucella species, confirming the divergence of B. ovis from these species. OMP10 and OMP19 were produced in recombinant Escherichia coli and purified to homogeneity for serological analysis. A large fraction of sera from sheep naturally infected with Brucella melitensis were reactive with these proteins in an enzyme-linked immunosorbent assay, whereas sera from B. abortus-infected cattle were almost completely unreactive in this assay.