Evaluation ofphoPandrpoSmutants ofSalmonella entericaserovar Typhi as attenuated typhoid vaccine candidates: virulence and protective immune responses in intranasally immunized mice

Abstract

The attenuation and immunoenhancing effects of rpoS and phoP Salmonella enterica serovar strain Typhi (Salmonella typhi) mutants have not been compared. Here, three S. typhi deletion mutants (phoP, rpoS, and rpoS-phoP double mutant) are constructed and these mutants are characterized with respect to invasiveness, virulence, and protective immune response compared with wild-type Ty2. It was found that phoP and phoP-rpoS deletion mutants are less invasive to HT-29 cells than the wild-type Ty2 and the rpoS single-deleted strain. The LD(50) of immunized mice was higher for phoP than for rpoS mutants, and the highest for the phoP-rpoS double mutant. In addition, all S. typhi mutants showed an increase in the specific serum IgG levels and T-cell-mediated immunity, and showed equal protection abilities against a wild-type Ty2 challenge after two rounds of immunization in BALB/c mice. It is concluded that phoP genes appear to play a more important role than rpoS genes in both cellular invasion and virulence of S. typhi, but not in immunogenicity in mice. Furthermore, the data indicate that the phoP-rpoS double mutant may show promise as a candidate for an attenuated typhoid vaccine.

Autoregulation of PhoP/PhoQ and Positive Regulation of the Cyclic AMP Receptor Protein-Cyclic AMP Complex by PhoP in Yersinia pestis

“…Expression of plasminogen activator (Pla), pesticin (Pst), and type III YOP secretion components is dependent on CRP in Y. pestis (11)(12)(13). Specifically, CRP directly stimulates the expression of Pla (11, 13), a virulence factor essential for bubonic and primary pneumonic plague (26,27).…”

“…CRP senses the switch of catabolites, and glucose may be the only free sugar that the bacteria can detect in hosts, whereas the presence of glucose stops the CRPcAMP machinery (10). Both PhoP and CRP are global regulators controlling complex cellular pathways, including multiple virulence determinants in Y. pestis (5,(11)(12)(13)(14)(15)(16).…”

Vi antigen of Salmonella enetrica serovar Typhi — biosynthesis, regulation and its use as vaccine candidate

“…While the role of rpoS in the S. Typhi virulence has not been explored extensively, studies have shown that rpoS gene might be involved in the S. Typhi virulence as the RpoS -strains of S. Typhi are less cytotoxic and survive better inside the resting THP-1 macrophages without induction of apoptosis than RpoS + strains [63]. A mutation in rpoS renders S. Typhi less cytotoxic to THP-1 macrophages and although the mutants survive similarly as in wild-type strain; the mutants were less invasive to epithelial cells [64]. Recent studies indicated that the allelic state of the rpoS gene and over-expression of Vi antigen are correlated.…”

A Tale of 6 Sigmas: How Changing Partners Allows Salmonella to Thrive in the Best of Times and Survive the Worst of Times

“…Mutants with a double knockout of the RpoS and PhoP/PhoQ show decreased virulence and decreased invasion of host cells (Lee et al, 2007). It has even been suggested that because of their inability to cause lasting infections, these double knockouts should be used to make a Salmonella vaccine (Lee et al, 2007).…”