The Brucella melitensis M5-90ΔmanB live vaccine candidate is safer than M5-90 and confers protection against wild-type challenge in BALB/c mice

Brucellosis is a globally distributed zoonotic disease that causes animal and human diseases. Although effective, the current Brucella vaccines (strain M5-90 or others) have several drawbacks. The first is their residual virulence for animals and humans and the second is their inability to differentiate natural infection from that caused by vaccination. In the present study, Brucella melitensis M5-90 manB mutant (M5-90ΔmanB) was generated to overcome these drawbacks. M5-90ΔmanB showed significantly reduced survival in macrophages and mice, and induced strong protective immunity in BALB/c mice. It elicited anti-Brucella-specific IgG1 and IgG2a subtype responses and induced the secretion of gamma interferon (IFN-γ) and interleukin-4(IL-4). Results of immune assays showed, M5-90ΔmanB immunization induced the secretion of IFN-γ in goats, and serum samples from goats inoculated with M5-90ΔmanB were negative by Bengal Plate Test (RBPT) and Standard Tube Agglutination Test (STAT). Further, the ManB antigen also allows serological assays differentiate infections caused by wild strains from infections by vaccination. These results show that M5-90ΔmanB is a suitable attenuated vaccine candidate against virulent Brucella melitensis 16 M (16 M) infection.