Evaluation of novel Brucella melitensis unmarked deletion mutants for safety and efficacy in the goat model of brucellosis

Abstract Pregnant goats were employed to assess unmarked deletion mutant vaccine candidates BMΔ asp24 , BMΔ cydBA , and BMΔ virB2 , as the target host species naturally infected with Brucella melitensis . Goats were assessed for the degree of pathology associated with the vaccine strains as well as the protective immunity afforded by each strain against abortion and infection after challenge with wild-type Brucella melitensis 16M. Both BMΔ asp24 and BMΔ virB2 were considered safe vaccine candidates in the pregnant goat model because they did not cause abortion or colonize fetal tissues. BMΔ asp24 was isolated from the maternal tissues only, indicating a slower rate of clearance of the vaccine strain than for BMΔ virB2 , which was not isolated from any maternal or fetal tissues. Both strains were protective against abortion and against infection in the majority of pregnant goats, although BMΔ asp24 was more efficacious than BMΔ virB2 against challenge infection.