Brucella abortus cyclic beta-1,2-glucan mutants have reduced virulence in mice and are defective in intracellular replication in HeLa cells

Null cyclic beta -1,2-glucan synthetase mutants legs mutants) were obtained from Brucella abortus virulent strain 2308 and from B. abortus attenuated vaccinal strain S19, Both mutants show greater sensitivity to surfactants l ike deoxycholic acid, sodium dodecyl sulfate, and Zwittergent than the pare ntal strains, suggesting cell surface alterations. Although not to the same extent, both mutants display reduced virulence in mice and defective intra cellular multiplication in HeLa cells. The B, abortus S19 cgs mutant was co mpletely cleared from the spleens of mice after 4 weeks, while the 2308 mut ant showed a 1.5-log reduction of the number of brucellae isolated from the spleens after 12 weeks, These results suggest that cyclic beta -1,2-glucan plays an important role in the residual virulence of the attenuated B, abo rtus S19 strain, Although the cgs mutant was cleared from the spleens earli er than the wild-type parental strain (B, abortus 819) and produced less in flammatory response, its ability to confer protection against the virulent strain B, abortus 2308 was fully retained. Equivalent levels of induction o f spleen gamma interferon mRNA and anti-lipopolysaccharide (LPS) of immunog lobulin G2a (IgG2a) subtype antibodies were observed in mice injected with B. abortus S19 or the cgs mutant. However, the titer of anti-LPS antibodies of the IgG1 subtype induced by the cgs mutant was lower than that observed with the parental 819 strain, thus suggesting that the cgs mutant induces a relatively exclusive Th1 response.