Salmonella serogroups

K. Bock and M. Meldal, Synthesis of tetrasaccharides related to the O-specific determinants of Salmonella serogroups A, B, and Dp Acta Chem. Scand. B. 38 255 (1984). 

Approximately 400 different glycosyltransferases are necessary in order to ensure the synthesis of those bacterial polysaccharides whose structures have thus far been elucidated. This estimate is based on the results of an analysis of the structures, made in order to ascertain how many different disaccharide fragments are present. An example of such an analysis is shown in Table V for the disaccharide sequences L-rhamnopyranosyl-D-galacto-pyranose, D-mannopyranosyl-L-rhamnopyranose, and D-galactopyranosyl-D-mannopyranose that are characteristic for the O-specific polysaccharides of Salmonella serogroups A, B, D, and E, the objects of many biosynthetic studies. Full details of similar analyses for other disaccharide sequences will be published elsewhere, as the resulting Tables are too voluminous for inclusion in this Chapter, but the most interesting results are summarized in Tables VI and VII. 

Incorporation of abequosyl side-chains in O-specific polysaccharides (12) of Salmonella serogroup B occurs at the stage of repeating-unit assembly. The polyprenyl trisaccharide diphosphate 16a serves as an acceptor for abequosyl transfer from its CDP derivative.83,307 A similar reaction was demonstrated with an enzyme preparation from Citrobacter.290 Polymerases from S. typhimurium83,308 and S. bredeney286 were able to act on the derivatives of linear trisaccharide 16a, but, in the former case, the efficiency of... 

Another example of O-specific polysaccharides that are assembled through the block mechanism are the polymers from Salmonella serogroups C2 and C3. Their polysaccharide chains (18) are composed97 of linear, tetrasaccharide repeating-units having abequosyl and D-glucosyl branches,... 

Preparation of modified, bacterial polysaccharides having monosaccharide analogs inserted into the polymeric chain is of interest for study of the structure-properties relationship in these biopolymers. Incorporation of chemically prepared, modified, biosynthetic precursors of the polymers in enzymic reactions seems a promising approach for achieving this aim. Such an approach, which may be termed chemical-enzymic synthesis, has now been studied by our group,439-441 using O-specific polysaccharides (10-12) of Salmonella serogroups B and E as an example. 

Specificity of the Enzymes of Biosynthesis of Polyprenyl Diphosphate Trisaccharides in Salmonella Serogroups B and E towards the Structure of the Monosaccharide Residues of Substrates... 

The chemical-enzymic approach to the synthesis of modified polysaccharides presents a good prospect for the preparation of small quantities of these polymers, which may prove very useful for immunochemical studies. The approach is certainly not limited by the specific case of Salmonella polysaccharides 10-12, and may well be extended to other polymers. The first results from this group322 show that several analogs of O-specific polysaccharides (18) of Salmonella serogroups C2 and C3 may be prepared through this approach. 

Thus it could safely be assumed that the PM-ITC-BSA antiserum was specific for the PM dlsaccharlde structure as found in Salmonella serogroup A bacteria. 

The disaccharide was synthesized as its -nltrophenyl derivative and subsequently, as described above, covalently linked to BSA to yield the glycoconjugate AR-BSA (18). Immunized rabbits responded with antibody production with specificity for the saccharide hapten, as demonstrated in ELISA studies (19). When tested in immunofluorescence, the AR-BSA antiserum proved to be of the same excellent specificity for the identification of Salmonella serogroup C2-C3 bacteria as had been shown previously for the other dldeoxyhexose-contalnlng dlsaccharlde haptens (Figure 1) (19). 

The structure of the O-antigenic polysaccharide chain in Salmonella serogroup Cl (0 antigens 6, 7) has not been established in detail (22). Hence, it has not been possible to identify the structural elements representing the determinant of serogroup 0-antigen 07. 

Within the Cl oligosaccharide hapten it is likely that several different regions elicit complementary antibodies. Hopefully, further structural studies and the synthesis of a few oligosaccharides may help us identify an 07 antigenic determinant with even higher specificity for Salmonella serogroup Cl. 

Exploratory studies using 18 different phages active on Salmonella serogroups A, B and D revealed that in effect all phages had hydrolytic activity and that all of them shared specificity for the L-Rhaj>(al 3)D-Galj> linkage (33, 36-38). There are, however, minor differences in terms of enzyme specificity. 

Figure 9. Titration of human sera in ELISA against LPSfrom (a) S. paratyphi A (02, 12), (b) S. typhimurium (04,5,12), and(c) S. typhi (09, 12). Key (a,b,c,) B, 12patients with Salmonella serogroup B infection D, 41 patients with Salmonella serogroup D infection and Bd, 36 healthy blood donors. The horizontal bars indicate the 95% confidence limits. (Reproduced with permission from Ref 50. Copyright 1975, Int. Arch.

The structures of the O-antigens of Salmonella serogroups A, B, D, and E were amongst the first to be studied structurally [11] and biosynthetically [12, 13]. These serogroups also comprise by far the largest clinically important group of Salmonella responsible for gastrointestinal infections [2]. 

T. Iversen and D. R. Bundle, Antigenic determinants of Salmonella serogroups and D,. Synthesis of trisaccharide glycosides for use as artificial antigens, Carbohydr. Res., 103 (1982) 29-40. 

G. I. Birnbaum and D. R. Bundle, Conformation of methyl 3,6-dideoxy-a-D-ara6/no-hexopy-ranoside, the inmunodominant sugar of Salmonella serogroup Dj Crystal structure, 111 nmr analysis, and semi-empirical calculations, Can. J. Chem., 63 (1985) 739-744. 

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