PCR assay for detecting B. abortus vaccine RB51 a brucellosis diagnosis that detects the presence of B. abortus vaccine RB51. YH, YL, ZX Brucella abortus vaccine strain RB51 is a natural stable attenuated rough mutant derived from the virulent strain 2308. The genetic mutations that are responsible for the roughness and the attenuation of strain RB51 have not been identified until now. It was demonstrated that the wboA gene encoding a glycosyltransferase, an enzyme essential for the synthesis of O antigen, is disrupted by an IS711 element in B. abortus vaccine strain RB51. The PCR assay developed here can distinguish strain RB51 from all other Brucella species and strains tested. PCR assay for brucellosis