Development of a New Live Rough Vaccine Against Bovine Brucellosis

Abstract

Brucella abortus S19 is the most commonly used attenuated live vaccine to prevent bovine brucellosis. In spite of its advantages, S19 has several drawbacks: it is abortive for pregnant cattle, is virulent for humans, and re-vaccination is not advised due to the persistence of anti-lipopolysaccharide (LPS) antibodies that hamper the immunoscreening procedures. For these reasons, there is a continuous search for new bovine vaccine candidates. We have previously characterized the phenotype of the phosphoglucomutase (pgm) gene disruption in Brucella abortus S2308, as well as the possible role for the smooth LPS in virulence and intracellular multiplication. Here we evaluate the vaccine properties of an unmarked deletion mutant of pgm. Western blot analysis of purified lipopolysaccharide and whole-cell extract from Delta pgm indicate that it synthesizes O-antigen but is incapable of assembling a complete LPS. In consequence Delta pgm has a rough phenotype. Experimental infections of mice indicate that Delta pgm is avirulent. Vaccination with Delta pgm induces protection levels comparable to those induced by S 19, and generates a splenocyte proliferative response and cytokines profile typical of a Th-1 response. The ability of the mutant to generate a strong cellular Th-1 response without eliciting specific O-antigen antibodies highlights the potential use of this mutant as a new live vaccine for cattle.