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Clin. Vaccine Immunol. doi:10.1128/CVI.00374-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

VirB12 is a serological marker of Brucella infection in experimental and natural hosts

University of California, Department of Medical Microbiology & Immunology, One Shields Avenue, Davis, CA 95616; Texas A&M University College Of Veterinary Medicine, Department of Veterinary Pathobiology, College Station, TX 77843-4467

^* To whom correspondence should be addressed. Email: rmtsolis{at}ucdavis.edu.

	Abstract

The Brucella species type IV secretion system (T4SS), encoded by the virB1-12 locus, is required for intracellular replication and persistent infection in vivo. The requirement of VirB proteins for infection suggests that they are expressed in vivo and may therefore represent serologic markers of infection. To test this idea, we purified recombinant VirB1, VirB5, VirB11, and VirB12 and tested their antibody recognition in sera from experimentally infected mice and goats, using an indirect enzyme-linked immunosorbent assay (ELISA). Antibody responses to VirB12, but not to VirB1, VirB5 or VirB11 were detected in 20/20 mice experimentally inoculated with B. abortus and 12/12 goats experimentally infected with B. melitensis. The potential use of VirB12 as a serological tool for the diagnosis of brucellosis was evaluated in the natural bovine host. Serum samples from 145 cattle of known serology (29% negative and 71% positive) were analyzed for the production of antibody response to VirB12. One hundred and two cattle samples (70.3%) were positive for antibodies to VirB12, while 43 samples were negative (29.7%). A positive serological response to VirB12 correlated with positive serology to whole B. abortus antigen in 99% of samples tested. These results show that VirB12 is expressed during infection of both experimental and natural hosts of Brucella species, and suggest that VirB12 may be a useful serodiagnostic marker for brucellosis.