Construction of an attenuated Salmonella enterica serovar Paratyphi A vaccine strain harboring defined mutations in htrA and yncD

Abstract

The global epidemic features of enteric fever have changed greatly in recent years. The incidence of enteric fever caused by Salmonella enterica serovar Paratyphi A has progressively increased. In some areas of Asia, infections with S. Paratyphi A have exceeded those with S. Typhi, resulting in S. Paratyphi A becoming the main causative agent of enteric fever. However, two currently licensed typhoid vaccines do not confer adequate cross-protection against S. Paratyphi A infection. Therefore, development of specific vaccines against enteric fever caused by S. Paratyphi A is urgently needed. In the present study, an attenuated strain was constructed by double deletion of the htrA and yncD genes in a wild-type strain of S. Paratyphi A and its safety and immunogenicity assessed. In a mouse model, the 50% lethal dose of the double deletion mutant and the wild-type strain were 3.0 Â 10 8 CFU and 1.9 Â 10 3 CFU, respectively, suggesting that the double deletion resulted in remarkably decreased bacterial virulence. Bacterial colonization of the double deletion mutant in the livers and spleens of infected mice was strikingly less than that of the wild-type strain. A single nasal administration of the attenuated vaccine candidate elicited high concentrations of anti-LPS and anti-flagellin IgG in a mouse model and protected immunized mice against lethal challenge with the wild-type strain. Thus, our findings suggest that the attenuated vaccine strain is a promising candidate worthy of further evaluation both as a human enteric fever vaccine and as a vaccine delivery vector for heterologous antigens.

Vi Capsular Polysaccharide Produced by Recombinant Salmonella enterica Serovar Paratyphi A Confers Immunoprotection against Infection by Salmonella enterica Serovar Typhi

“…PhoPQ serves as a two-component regulatory system, which regulates the expression of several virulence genes, and plays a crucial role in pathogenesis (Miller et al, 1989). Both htrA and phoPQ have been extensively used in attenuating bacteria (Galán and curtiss, 1989; Chatfield et al, 1992; Karasova et al, 2009; Singh et al, 2013; Zhu et al, 2015). …”

Paratyphoid Fever A: Infection and Prevention

“…The double deletion mutant was completely inhibited when grown at 46 • C, while the wild-type and the yncD mutant grew well at the same temperature. Moreover, when exposed to hydrogen peroxide, the growth of the double deletion mutant was strikingly decreased relative to the wild-type and the yncD mutant (Zhu et al, 2015). The virulence of the double deletion mutant was reduced by 1.58 × 10 5 times compared with the parent strain.…”

“…Deficiency of the HtrA protein leads to decreased virulence in many pathogenic bacteria (Skorko-Glonek et al, 2013). Zhu et al (2015) constructed a mutant of S. Paratyphi A by deleting htrA and yncD. The double deletion mutant was completely inhibited when grown at 46 • C, while the wild-type and the yncD mutant grew well at the same temperature.…”

“…The virulence of the double deletion mutant was reduced by 1.58 × 10 5 times compared with the parent strain. Nasal immunization of the attenuated strain protected immunized mice against the lethal challenge of the wild-type strain (Zhu et al, 2015).…”

Application of TonB-Dependent Transporters in Vaccine Development of Gram-Negative Bacteria

“…Nasal inoculation of the yncD-deleted mutant elicited a significant immunoprotection against the lethal wild-type challenge (Xiong et al, 2012). The yncD gene was also used in the construction of the attenuated vaccine strains of S. Paratyphi A (Xiong et al, 2015;Zhu et al, 2015).…”