Immunochemical and structural analysis of the O polysaccharides of Salmonella zuerich [1,9,27,(46)].

Salmonella zuerich [1,9,27,(46)] has been shown to exhibit two levels of structural heterogeneity. The bacterium carries two distinct O-polysaccharide molecules with and without O:factor 1. Both sets of molecules (1+ and 1-) carry the two O:factors 27 and 46 on the same O chain, but they are expressed unevenly; in contrast to factor 27, O:factor 46 is always weakly expressed. Part of this weak expression was thought to be due to strong inhibition of factor 46 by factor 1. In this study, serological analysis gave more detailed information on the sizes of the different O:factor epitopes. Structural analysis of S. zuerich O polysaccharides showed that they are constructed of the expected chemical sequences characteristic of factors 1, 9, 27, and 46. No modification in the sugar sequence could account for the weak expression of O:factor 46. Factors 27 and 46 are present on oligosaccharides carrying either an alpha-Man (factor 27) or a beta-Man (factor 46) residue. In S. zuerich, the alpha-Man configuration is predominant, corroborating the expression of strong factor 27 and weak factor 46 on the bacteria. Questions raised by the existence of such heterogeneous O polysaccharides on the specificity of the O chain polymerase, as well as the place of S. zuerich in Salmonella evolution, are dicussed in this paper.