Development of an auxotrophic, live-attenuated Brucella suis vaccine strain capable of expressing multimeric GnRH

Evaluation of Brucellosis Vaccines: A Comprehensive Review

Brucellosis is a bacterial zoonosis caused by Brucella spp. which can lead to heavy economic losses and severe human diseases. Thus, controlling brucellosis is very important. Due to humans easily gaining brucellosis from animals, animal brucellosis control programs can help the eradication of human brucellosis. There are two popular vaccines against animal brucellosis. Live attenuated Brucella abortus strain 19 (S19 vaccine) is the first effective and most extensively used vaccine for the prevention of brucellosis in cattle. Live attenuated Brucella melitensis strain Rev.1 (Rev.1 vaccine) is the most effective vaccine against caprine and ovine brucellosis. Although these two vaccines provide good immunity for animals against brucellosis, the expense of persistent serological responses is one of the main problems of both vaccines. The advantages and limitations of Brucella vaccines, especially new vaccine candidates, have been less studied. In addition, there is an urgent need for new strategies to control and eradicate this disease. Therefore, this narrative review aims to present an updated overview of the available different types of brucellosis vaccines.

Development of attenuated live vaccine candidates against swine brucellosis in a non-zoonotic B. suis biovar 2 background

Brucella is a genus of gram-negative bacteria that cause brucellosis. B. abortus and B. melitensis infect domestic ruminants while B. suis (biovars 1-3) infect swine, and all these bacteria but B. suis biovar 2 are zoonotic. Live attenuated B. abortus S19 and B. melitensis Rev1 are effective vaccines in domestic ruminants, though both can infect humans. However, there is no swine brucellosis vaccine. Here, we investigated the potential use as vaccines of B. suis biovar 2 rough (R) lipopolysaccharide (LPS) mutants totally lacking O-chain (Bs2ΔwbkF) or only producing internal O-chain precursors (Bs2Δwzm) and mutants with a smooth (S) LPS defective in the core lateral branch (Bs2ΔwadB and Bs2ΔwadD). We also investigated mutants in the pyruvate phosphate dikinase (Bs2ΔppdK) and phosphoenolpyruvate carboxykinase (Bs2ΔpckA) genes encoding enzymes bridging phosphoenolpyruvate and the tricarboxylic acid cycle. When tested in the OIE mouse model at the recommended R or S vaccine doses (10⁸ and 10⁵ CFU, respectively), CFU/spleen of all LPS mutants were reduced with respect to the wild type and decreased faster for the R than for the S mutants. At those doses, protection against B. suis was similar for Bs2ΔwbkF, Bs2Δwzm, Bs2ΔwadB and the Rev1 control (10⁵ CFU). As described before for B. abortus, B. suis biovar 2 carried a disabled pckA so that a double mutant Bs2ΔppdKΔpckA had the same metabolic phenotype as Bs2ΔppdK and ppdK mutation was enough to generate attenuation. At 10⁵ CFU, Bs2ΔppdK also conferred the same protection as Rev1. As compared to other B. suis vaccine candidates described before, the mutants described here simultaneously carry irreversible deletions easy to identify as vaccine markers, lack antibiotic-resistance markers and were obtained in a non-zoonotic background. Since R vaccines should not elicit antibodies to the S-LPS and wzm mutants carry immunogenic O-chain precursors and did not improve Bs2ΔwbkF, the latter seems a better R vaccine candidate than Bs2Δwzm. However, taking into account that all R vaccines interfere in ELISA and other widely used assays, whether Bs2ΔwbkF is advantageous over Bs2ΔwadB or Bs2ΔppdK requires experiments in the natural host.

Rough Brucella neotomae provides protection against Brucella suis challenge in mice

Brucellosis is one of the most common zoonotic diseases worldwide. Almost 500,000 new human cases occur each year; yet there is no vaccine for human use. Moreover, there is no universal Brucella vaccine that would provide protection against all pathogenic species of Brucella. We generated a rough, live-attenuated B. neotomae strain by deleting the wboA gene encoding a glycosyltransferase. This strain lacks the O-side chain in its lipopolysaccharide (LPS) and thus the vaccinated animals can be differentiated serologically from the field-infected animals. We tested the efficacy of rough B. neotomae strain to stimulate dendritic cells compared to the smooth wild type strain. Based on TNF-α production, our data suggests that a significantly higher stimulation was obtained when dendritic cells were stimulated with the rough vaccine strain compared to the smooth wild type B. neotomae. Furthermore, the rough mutant was cleared from mice within 6 weeks even at a dose as high as 2 x 10⁸ CFU. Vaccinated mice showed significantly higher level of protection against a virulent B. suis 1330 challenge compared to the control mice. Antibody titers in the mice and cytokine production by the splenocytes from the vaccinated mice showed a Th1 mediated immune response that correlated with the protection.

Optimization and Comparison of Different Methods and Factors for Efficient Transformation of Brucella abortus RB51strain

Background:

The development of protective vaccines for Brucella spp. has been hampered by the difficulty in transformation of Brucella cells with foreign DNA for genetic manipulation. It seems that the formation of Brucella spheroplasts would increase the efficiency of transformation. The aim of this study was to devise an efficient method for the transformation of Brucella spp.

Materials and Methods:

At first, spheroplast of Brucella was prepared by glycine and ampicillin induction and transformed using optimized protocols of CaCl₂, electroporation, and lipofection methods. Then, the efficacy of transformation was compared between the three-mentioned methods.

Results:

Ampicillin-induced spheroplasts from early-log phase culture of brucella when incubated in a medium-containing 0.2 M sucrose during cell recovery had higher transformation efficiency in three different methods. Comparison of the transformation efficiency of Brucella abortus RB51 using the CaCl₂, lipofection, and electroporation methods revealed that the transformation efficiency with the lipofection method was significantly higher than with other two methods (P < 0.05).

Conclusions:

Lipofection method by lipofectamine 2000 on ampicillin-induced spheroplasts can be a suitable approach for Brucella transformation.