A New Live Auxotrophic Vaccine Induces Cross-Protection against Infections in Mice.

The development of a whole-cell vaccine from bacteria auxotrophic for D-amino acids present in the bacterial cell wall is considered a promising strategy for providing protection against bacterial infections. Here, we constructed a prototype vaccine, consisting of a glutamate racemase-deficient mutant, for preventing infections. The deletion mutant lacks the gene and requires exogenous addition of D-glutamate for growth. The results showed that the Δ strain is attenuated and includes a favourable combination of antigens for inducing a robust immune response and conferring an adequate level of cross-protection against systemic infections caused by strains, including some hypervirulent serotypes with elevated production of capsule polysaccharide as well as multiresistant strains. The auxotroph also induced specific production of IL-17A and IFN-γ. The rapid elimination of the strain from the blood of mice without causing disease suggests a high level of safety for administration as a vaccine.