Abstract
BackgroundEnterobacterial common antigen (ECA) is a family-specific surface antigen shared by all members of the Enterobacteriaceae family. Previous studies showed that the loss of ECA results in Salmonella attenuation, indicating its usefulness as a vaccine candidate for Salmonella infection, but no studies have shown whether the mutation resulting from the deletion of the ECA operon in conjunction with other mutations could be used as an antigen vehicle for heterologous protein antigen delivery.ResultsIn this study, we introduced a nonpolar, defined ECA operon deletion into wild-type S. Typhimurium χ3761 and an attenuated vaccine strain χ9241, obtaining two isogenic ECA operon mutants, namely, χ12357 and χ12358, respectively. A number of in vitro and in vivo properties of the mutants were analyzed. We found that the loss of ECA did not affect the growth, lipopolysaccharide (LPS) production and motility of S. Typhimurium wild type strain χ3761 and its attenuated vaccine strain χ9241 but significantly affected the virulence when administered orally to BALB/c mice. Furthermore, the effects of the ECA mutation on the immunogenicity of a recombinant S. Typhimurium vaccine strain χ9241 when delivering the pneumococcal antigen PspA were determined. The result showed that the total anti-PspA IgG level of χ12358 (pYA4088) was slightly lower than that of χ9241 (pYA4088), but the protection rate was not compromised.ConclusionsECA affects virulence and benefits the Th2 immunity of Salmonella Typhimurium, therefore, it is feasible to use a reversible ECA mutant mode to design future Salmonella vaccine strains for heterologous protective antigens.
Highlights
Enterobacterial common antigen (ECA) is a family-specific surface antigen shared by all members of the Enterobacteriaceae family
A pair of primers, Doperon-1F/Doperon-2R, were used to amplify the ECA operon from χ 3761 and χ12357, and a PCR product of approximately 800 bp could be observed for χ12357, but no bands were observed for χ3761 in agarose gel, which indicated that mutants with deletion of the ECA operon were created in χ12357 (Fig. 1c)
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]
Summary
Enterobacterial common antigen (ECA) is a family-specific surface antigen shared by all members of the Enterobacteriaceae family. Enterobacterial common antigen (ECA) is a kind of unique glycolipid on the cell surface of all Enterobacteriaceae family members, such as Klebsiella, Proteus, Shigella, Yersinia, and Salmonella [1,2,3,4]. It consists of linear repetitive units of a trisaccharide composed of 4-acetamide-4,6dideoxy-D-galactose (Fuc4NAc), N-acetyl-D-mannosaminuronic acid (ManNAcA), and N-acetyl-D-glucosamine (GlcNAc). Similar with O-antigen, ECAs are polysaccharide antigens anchored on the surface of bacteria cells and can trigger the production of anti-ECA antibodies in mice These anti-ECA antibodies hardly account for the passive immune protection against these Enterobacteriaceae strains, which distinguish from other virulence factors and surface polysaccharides. The avoidance of triggering anti-ECA antibody production in the host by the Salmonella vaccine may contribute to increased stimulation of the immune response against heterologous antigens
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