Recombinant bacterium capable of eliciting an immune response against

1. A recombinant Salmonella enterica serovar Typhi bacterium, comprising

(a) regulated expression of at least one nucleic acid encoding at least two Streptococcus pneumoniae antigens and comprises

(i) at least one nucleic acid sequence encoding a repressor operably linked to a regulatable promoter,

wherein the repressor is selected from the group consisting of Lacl, C2, and C1, and

the regulatable promoter is selected from the group consisting of PBAD, a promoter regulated by maltose, a promoter regulated by rhamnose, and a promoter regulated by xylose, and

(ii) at least one nucleic acid sequence encoding at least two S. pneumoniae antigens operably linked to a promoter regulated by the repressor such that the expression of the nucleic acid sequence encoding the S. pneumoniae antigens is repressed during in vitro growth of the recombinant bacterium, but the recombinant bacterium is capable of high level expression of the nucleic acid sequence encoding the S. pneumoniae antigens in vivo;

(b) regulated attenuation and comprises

(i) a first mutation selected from the group consisting of a crp mutation, a fur mutation, and phoPQ mutation such that expression of the nucleic acid sequence encoding crp, fur, or phoPQ is repressed during in vivo growth but the recombinant bacterium is capable of high level expression of the nucleic acid in vitro, and

(ii) a second mutation selected from the group consisting of an rfc mutation such that LPS O-antigen synthesis is greater during in vitro growth compared to in vivo growth of the recombinant bacterium, a pmi mutation that results in lack of function of the pmi gene product, and a galE mutation that results in lack of function of the galE gene product;

(c) decreased persistence in the gastrointestinal tract of a host and comprises a mutation selected from the group consisting of a Vi capsular antigen mutation that reduces synthesis of the Vi capsular antigen, a mutation that reduces synthesis of colanic acid, a mutation that reduces synthesis of thin aggregative fimbriae, a mutation that reduces synthesis of cellulose, a mutation that reduces synthesis of extracellular polysaccharide, or a combination thereof; and

(d) reduced fluid secretion in the gastrointestinal tract of a host and comprises a mutation selected from the group consisting of a sopB mutation that reduces synthesis of SopB and a pagP mutation that reduces synthesis of PagP.

2. The recombinant bacterium of claim 1 , further comprising a RpoS-mutation.

3. The recombinant bacterium of claim 1 , wherein the bacterium comprises a first mutation conferring regulated attenuation selected from the group consisting of a ΔP crp ::TT araC P BAD crp mutation, a ΔP fur ::TT araC P BAD fur mutation, and a ΔP phoPQ ::TT araC P BAD phoPQ mutation, and a second mutation conferring regulated attenuation selected from the group consisting of a ΔP rfc ::TT araC P BAD rfc mutation, a Δpmi mutation, and a ΔgalE mutation.

4. The recombinant bacterium of claim 1 , wherein the bacterium comprises a Vi capsular antigen mutation that reduces synthesis of the Vi capsular antigen, and at least one mutation selected from the group consisting of a mutation that reduces synthesis of colanic acid, a mutation that reduces synthesis of thin aggregative fimbriae, a mutation that reduces synthesis of cellulose, a mutation that reduces synthesis of extracellular polysaccharide.

5. The recombinant bacterium of claim 1 , wherein the bacterium comprises a ΔpagP::P ipp IpxE mutation or a ΔsopB mutation.

6. The recombinant bacterium of claim 1 , wherein the bacterium comprises

(a) a ΔrelA::araC P BAD lacl TT mutation and at least one nucleic acid sequence encoding at least two S. pneumoniae antigens operably linked to a promoter regulated by Lacl;

(b) a first mutation conferring regulated attenuation selected from the group consisting of a ΔP crp ::TT araC P BAD crp mutation, a ΔP fur ::TT araC P BAD fur mutation, and a ΔP phoPQ )::TT araC P BAD phoPQ mutation, and a second mutation conferring regulated attenuation selected from the group consisting of a ΔP rfc ::TT araC P BAD rfc mutation, a Δpmi mutation, and a ΔgalE mutation;

(c) at least one mutation selected from the group consisting of a ΔtviABCDE mutation, a ΔtviBCDE mutation, a Δ(gmd-fcl) mutation, a Δ(wza-wcaM) mutation, a ΔagfBAC mutation, a Δ(agfC-agfG) mutation, a ΔbcsABZC mutation, a ΔbcsEFG mutation, and a Δ(yshA-yihW) mutation; and

(d) at least one mutation selected from the group consisting of a ΔsopB mutation and a ΔpagP::P lpp IpxE mutation.

7. A vaccine composition, the composition comprising a bacterium of claim 1 .

8. The recombinant bacterium of claim 1 , wherein the bacterium comprises (i) a mutation selected from the group consisting of a ΔtviABCDE mutation, a ΔtviBCDE mutation, a Δ(gmd-fcl) mutation, and a Δ(wza-wcaM) mutation, and (ii) a mutation selected from the group consisting of a ΔagfBAC mutation, a Δ(agfC-agfG) mutation, a ΔbcsABZC mutation, a ΔbcsEFG mutation, and a Δ(yshA-yihW) mutation.

9. The recombinant bacterium of claim 1 , wherein the bacterium is derived from an RpoS-strain and has a restored rpoS gene.

10. The recombinant bacterium of claim 1 , wherein the at least two S. pneumoniae antigens are independently selected from the group consisting of PspA, PspC, Ply, PcsB, PsaA, StkP, a PspA fusion, and a PspC fusion, wherein the PspA fusion comprises sequences from two or more PspA antigen families and the PspC fusion comprises sequences from two or more PspC antigen families.