Abstract: To develop a novel marker brucellosis vaccine, the gene-deleted mutant RB6 derived from Brucella abortus was used in this paper to examine its essential properties. By comparing growth characteristics, staining properties, agglutination identities, stability, virulence and immunological protection between RB6 and its parent strain, it was found that the growth characteristics of RB6 was similar to the parent strain, but the colonies on TSA became to the violet in the crystal violet staining test, and the cultural suspension was agglutinated with sera against Brucella rough-type strain, which showed that RB6 was a rough phenotype. It was also demonstrated that the phenotype and virulence of RB6 was stable when it was subcultured for 20 passages in vitro and then for 5 passages in heifers. In the mice model, RB6 was attenuated and induced the similar immunological protection levels as A19 vaccine strain. In a word, RB6 was a rough-type mutant with low virulence, high genetic stability and good protection efficacy, which could be employed to prepare new marker vaccines using for the prevention and control of animal brucellosis.

Key words: Brucella abortus; rough-type vaccine; stability; virulence; immune efficacy