Chemie bakterieller O-Antigene

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Abstract
The O-antigens of Gram-neg.bacteria are closely connected with the endotoxic complexes which are constituents of the bacterial cell wall. The main part of bacterial O-antigens is the species- or group-specific polysaccharide. Analyses in the family Enterobacteriaceae revealed that many different sugars take part in the constitution of their specific polysaccharides: hexosamines, heptoses, hexoses, pentoses, 6-deoxy-hexoses and 3 6-dideoxy-hexoses. On the basis of precipitation inhibition studies (A. M. Staub et al.) the sugars acting as the determinant endogroups of many O-antigen factors of the Kauffmann-White scheme of Salmonellae were estimated. 3.6-Dideoxy-hexoses often play an important role as determinant endgroups in the highly branched enterobacterial polysaccharides. Immunization of goats with an artificial antigen containing colitose (3-deoxy- L-fucose) as the determinant group- colitose-a-phenylazo-protein[long dash]stimulated the production of anti-colitose antibodies which cross-reacted with some colitose-containing bacterial polysaccharides (E_. coli O 111, Arizona 20, Salmonella O 35) and agglutinated the respective bacteria (A. M. Staub et al.). Extensive analyses of many Salmonella O-antigens (F. Kauffmann) revealed a close relation between serotypes and chemotypes. Members of the same O serogroup were always found to belong to the same chemotype. In the Salmonellae the O-antigens (lipopolysaccharides) can be chemically classified by placing them into 16 chemotypes (I-XVI), i.e. sugar composition. The simplest chemotype I is given by a composition of 4 sugars: glucoseamine, heptose, galactose and glucose. The other chemotypes II-XVI are more complicated with additional sugars. The highest chemotypes (XIV, XV, XVI) correspond to (lipo)polysac-charides with 7 sugars; O-antigens of these chemotypes are the most lipophilic ones and belong to Salmonella strains most frequently found in clinical cases. S[forward arrow] R variation in the genus Salmonella leads to the disappearance of the O-antigenic specificity and to cell wall polysaccharides (R-antigens) which are always of chemotype I, no matter to what chemotype the original S-form belonged. R-forms thus appear to be minus variants of the corresponding S-forms. A working hypothesis was developed, according to which all Salmonella S-forms synthesize a basic polysaccharide of chemotype I with R-character, to which side chains are added carrying the O-specific determinant groups.[long dash]On partial hydrolysis some Salmonella O-antigens gave rise to degraded polysaccharides with strong Salmonella R-specificity indicating that R-specificity is part of the intrinsic structure of these O-antigens. The R-antigens of many Salmonella R-strains exert serological cross-reactions, thus showing qualitative chemical and serologic similarity. Investigations with respect to the bloc of sugar and/or polysaccharide biosynthesis in bacteria, undergoing S [forward arrow] R change, are in progress (J. L. Strominger et al., and others). It is pointed out that the biosynthesis of the O-specific oligosaccharidic side chains in O-antigens is genetically controlled. Changes of O-antigen factors can be induced by aid of lysogenic phages (S. E. Luria, P. W. Robbins and others). It is emphasized that the enterobacterial and especially the Salmonella O-antigens with their many known specificities (Kauffmann-White scheme) offer an ideal field of researchfor immunochemists, biochemists and geneticists.