Construction and characterization of isogenic O‐antigen variants of Salmonella typhi

Abstract

A 7.5 kb KpnI-generated fragment, from within the rfb cluster of Salmonella typhimurium LT2 that encodes abequose synthase (the rfbJ gene) which is necessary for O4 antigen synthesis, and flanking sequences, was inserted into a suicide vector. Using allelic exchange techniques, these rfb sequences of S. typhimurium were integrated into the rfb clusters of wild-type Salmonella typhi Vi-positive strain ISP 1820 (i.e. serotype O9,12; Vi+; H-d), S. typhi Vinegative strain H400 (i.e. serotype O9,12; Vi-; H-d), and a double aro mutant of S. typhi ISP 1820, strain CVD 906, resulting in the isolation of strains H325, H404 and CVD 906-O4, respectively. Immunoblot analysis of lipopolysaccharide (LPS) purified from H325, H404 and CVD 906-O4 demonstrated that these strains express the O4 antigen (an abequose residue) in place of the O9 antigen (a tyvelose residue) in the LPS molecule. Hence, the serotype of H325 is O4,12; Vi+; H-d and the serotype of H404 is O4,12; Vi-; H-d. DNA hybridization analysis of chromosomal DNA from H325, H404 and CVD 906-O4 confirmed that a precise recombination event within sequences flanking rfbSE of S. typhi (which encodes the enzymes necessary for cytidine diphosphate-tyvelose synthesis) resulted in replacement of rfbSE with rfbJ (which encodes abequose synthase and is necessary for O4 synthesis) of S. typhimurium in strains H325, H404 and CVD 906-O4. The resistance of each strain to the bactericidal effects of guinea-pig serum (GPC) was assessed. Whereas ISP 1820, H325 and H404 exhibit similar resistance patterns in GPC, strain H400 is sensitive to the bactericidal effects of GPC.(ABSTRACT TRUNCATED AT 250 WORDS)

The Vi Capsular Polysaccharide Prevents Complement Receptor 3-Mediated Clearance of Salmonella enterica Serotype Typhi

“…2C). These data were consistent with those from previous reports showing that Vi capsule-negative S. Typhi isolates exhibit increased serum sensitivity (14). Introduction of the cloned tviABCDE vexABCDE genes (pDC5) into E. coli strain W3110 resulted in expression of the Vi capsular polysaccharide (Fig.…”

A biologically conjugated polysaccharide vaccine delivered by attenuated Salmonella Typhimurium provides protection against challenge of avian pathogenic Escherichia coli O1 infection

“…While this method can provide genetic stability of O-antigen gene cluster in the host, it still requires long PCR, digestion and ligation, and the efficacy of this method is low (Goldberg et al 1992;Roland, Curtiss and Sizemore 1999). Phage carrying O-antigen gene clusters may also be exploited to switch the O-serotype within the same species, such as in Salmonella enterica, but this approach is difficult to manipulate (Hone et al 1994).…”

A deletion in the sapA homologue cluster is responsible for the loss of the S-layer in Campylobacter fetus strain TK

“…For example, Neisseria meningitidis and Neisseria gonorrhoeae generate antigenic variations of their pili by transposing structural genes to an expression sequence containing the promoter and start codon (Zhang et al 1992;Wainwright et al 1994). Salmonella changes its flagella proteins by inducing the inversion control of gene expression (Hone et al 1994). Trypanosomes switch their coat composition by gene conversion or homologous recombination that leads to promoter addition (Borst and Rudenko 1994).…”