The Brucella abortus S19 Δ vjbR Live Vaccine Candidate Is Safer than S19 and Confers Protection against Wild-Type Challenge in BALB/c Mice When Delivered in a Sustained-Release Vehicle

Abstract

Brucellosis is an important zoonotic disease of nearly worldwide distribution. Despite the availability of live vaccine strains for bovine (S19, RB51) and small ruminants (Rev-1), these vaccines have several drawbacks, including residual virulence for animals and humans. Safe and efficacious immunization systems are therefore needed to overcome these disadvantages. A vjbR knockout was generated in the S19 vaccine and investigated for its potential use as an improved vaccine candidate. Vaccination with a sustained-release vehicle to enhance vaccination efficacy was evaluated utilizing the live S19 ⌬vjbR::Kan in encapsulated alginate microspheres containing a nonimmunogenic eggshell precursor protein of the parasite Fasciola hepatica (vitelline protein B). BALB/c mice were immunized intraperitoneally with either encapsulated or nonencapsulated S19 ⌬vjbR::Kan at a dose of 1 ؋ 10 5 CFU per animal to evaluate immunogenicity, safety, and protective efficacy. Humoral responses postvaccination indicate that the vaccine candidate was able to elicit an anti-Brucella-specific immunoglobulin G response even when the vaccine was administered in an encapsulated format. The safety was revealed by the absence of splenomegaly in mice that were inoculated with the mutant. Finally, a single dose with the encapsulated mutant conferred higher levels of protection compared to the nonencapsulated vaccine. These results suggest that S19 ⌬vjbR::Kan is safer than S19, induces protection in mice, and should be considered as a vaccine candidate when administered in a sustained-release manner.

Protective Efficacy and Safety of Brucella melitensis 16MΔmucRagainst Intraperitoneal and Aerosol Challenge in BALB/c Mice

“…When 16M⌬mucR vaccinated mice were challenged against wild-type B. melitensis 16M, all of the animals demonstrated a statistically significant reduction in the bacterial burden in the spleen, lung, and liver regardless of the vaccination dose. The marked reduction in bacterial burden in the spleen conferred by the mutant is impressive and comparable to other live attenuated vaccine candidates tested by this laboratory and others (2,20,21,25). Although an intraperitoneal challenge is of historical importance, a more logical approach is the use of an aerosol challenge route, not only because of the documented evidence of aerosol transmission of these organisms but also because of the potential threat of the use of Brucella as a bioterrorism agent (13,18,22,26).…”

“…Most importantly, protection against the most common microscopic changes associated with the disease in mice, such as granulomatous hepatitis, granulomatous splenitis, or splenomegaly, was not observed, indicating that vaccination with the mucR mutant not only reduced the bacterial burden in multiple organs but also prevents against the development of Brucella-associated pathological changes. Lack of splenomegaly associated with vaccination has been previously demonstrated as a safety parameter in other Brucella vaccine candidates (2).…”

Quorum-Sensing and BvrR/BvrS Regulation, the Type IV Secretion System, Cyclic Glucans, and BacA in the Virulence of Brucella ovis: Similarities to and Differences from Smooth Brucellae

“…(3,14). In contrast, survival of the ⌬vjbR mutant of the B. abortus S19 vaccine was only slightly attenuated in J774.A1 macrophages (2) and it showed levels of spleen infection and persistence in the mouse model similar to those of the parental strain and remarkably higher than those reported for the B. melitensis 16M mutant (2,3,14). These results suggest variability among the brucellae regarding the impact of VjbR on virulence, but other vjbR mutants should be obtained in the genus Brucella to clarify this point.…”

Extended Safety and Efficacy Studies of the Attenuated Brucella Vaccine Candidates 16MΔvjbRand S19ΔvjbRin the Immunocompromised IRF-1−/−Mouse Model

“…Strains used in these experiments include B. melitensis 16M⌬vjbR (engineered for a previous study and used as a vaccine candidate) (35), S19⌬vjbR (engineered for a previous study and used as a vaccine candidate) (2), B. abortus S19 (NVSL, Ames, IA), the virulent strain Brucella melitensis 16M biovar 1 (originally obtained from ATCC and reisolated by this lab from an aborted goat fetus) (2,12), and the wild-type strain Brucella abortus 2308 obtained from an aborted fetus by To prepare organisms for animal infections, the Brucella strains were harvested from the surface of the plates after 3 days of incubation using phosphate-buffered saline (PBS), pH 7.2 (Gibco). The bacteria were resuspended to a final concentration of 1 ϫ 10 6 CFU/mouse on the basis of optical density readings using a Klett meter and a standardized lightscattering curve.…”

“…VjbR is required for adequate VirB expression, which is essential for survival in phagocytes and virulence in mice (32). The vjbR mutants of B. melitensis and B. abortus are highly attenuated in mice and macrophages while conferring high levels of protective immunity, making such mutants ideal vaccine candidates (2,3).…”