An enterobacterial common antigen mutant of Salmonella enterica serovar Typhimurium as a vaccine candidate

Abstract

Due to increasing rates of invasive Salmonella enterica serovar Typhimurium infection, there is a need for an effective vaccine to prevent this disease. Previous studies showed that a mutation in the first gene of the Enterobacterial common antigen biosynthetic pathway, wecA, resulted in attenuation of S. Typhimurium in a murine model of salmonellosis. Furthermore, immunization with a wecA(-) strain protected against lethal challenge with the parental wild type S. Typhimurium strain. Herein, we examined whether the S. Typhimurium wecA(-) strain could also provide cross-protection against non-parental strains of S. Typhimurium and S. Enteritidis. We found that intraperitoneal immunization (IP) with S. Typhimurium SL1344 wecA(-) resulted in a significant increase in survival compared to control mice for all Salmonella challenge strains tested. Oral immunization with SL1344 wecA(-) also resulted in increased survival; however, protection was less significant than with intraperitoneal immunization. The increase in survival of SL1344 wecA(-) immunized mice was associated with a Salmonella-specific IgG antibody response. Furthermore, analysis of sera from IP and orally immunized animals revealed cross-reactive antibodies to numerous Salmonella isolates. Functional analysis of antibodies found within the sera from IP immunized animals revealed agglutination and opsonophagocytic activity against all tested O:4 Salmonella serovars. Together these results indicate that immunization with a S. Typhimurium wecA(-) strain confers protection against lethal challenge with wild type S. Typhimurium and S. Enteritidis and that immunization correlates with functional antibody production.

Effect of Deletion of Gene Cluster involved in Synthesis of Enterobacterial Common Antigen on Virulence and Immunogenicity of Live Attenuated Salmonella Vaccine when Delivering Heterologous Streptococcus pneumoniae Antigen PspA

“…Our studies proved the susceptibility of mutants carrying the ECA operon deletion to the bile salt deoxycholate, which is consistent with a previous report that mutations of wecA genes in Salmonella enhance the sensitivity to bile salts [11] . We also observed signi cant attenuation of the ECA operon mutants and persistent loading in mouse organs, consistent with previous reports [18,21].…”

“…Most mutations related to the loss of ECA are restricted to a single mutation, which are limited by the high possibility of reversible virulence and redundant genes presence in the genome, leading to a waste of energy and nutrients necessary for bacterial growth [18,21]. In this work, we constructed ECA-de cient S. Typhimurium mutants by deleting the entire ECA operon from wecA to wecG and evaluated the mutant strain for its virulence and ability to be used for heterologous antigen delivery.…”

“…When assessing the LD 50 and bacterial loading of the ECA-de cient strain in mice, we observed meningitis-like symptoms (head tilt, spinning and unidirectional motion) in a small portion of the mice that were orally administered a dose higher than 10 8 CFU of the ECA-de cient strain χ12357. While the ECA-de cient strain can still potentially be used to develop vaccines [21], to ensure the safety of live Salmonella vaccines, additional genetically unlinked mutations should be included in the vaccine strain to further attenuate these potential side effects. Therefore, Δ(wecA-wecG)-6 was combined with the ΔpabAB mutation in strain χ9241 to create vaccine strain χ12358 to evaluate the effects of ECA de ciency on immunogenicity by introducing plasmid pYA4088, which directs the synthesis of the heterologous pneumococcal protective antigen PspA [23,35].…”

“…In Salmonella Typhimurium, ΔwecA mutants are also more sensitive to bile and less lethal to mice. Due to the undesirable host immune response stimulated by ECAs, recent studies have revised the ECA of the Salmonella vaccine carrier to deliver O-antigen polysaccharide [21,22]. We demonstrated that downregulation of O-antigen expression could reduce the immune response against speci c O-antigen of attenuated Salmonella carriers while triggering a strong immune response against heterologous antigens [23][24][25], and downregulation of both O-antigen and ECA production in Salmonella enhances the immunogenicity and cross-protective e cacy against heterologous Salmonella challenge [26].…”

Heterologous Pseudomonas aeruginosa O-antigen delivery using a Salmonella enterica serovar Typhimurium wecA mutant strain

“…Typhimurium and S. Enteritidis challenge in a murine model of salmonellosis; IP immunization offered the highest level of protection (Bridge et al, 2015). Furthermore, immunization with SL1344…”