O-antigenic determinants in Salmonella species of serogroup C1 are expressed in distinct immunochemical populations of chains

The O-antigenic specificities found among salmonellae of serogroup C 1 are O:6 1, 7, O:6 2, 7, O:6 1, 6 2, 7 and O:6,7,14, as defined by classical serology. Factor O:7 is the group-wide determinant while factors O:6 1, O:6 2 and O:14 are found in some strains but not others. Strains of the O:6 2, 7 specificity are subject to lysogenic conversion by phages 6 1 and 14 to the O:6 1, 7 and O:6,7,14 specificities, respectively. To further delineate antigenic complexity and serological relationships among strains of this serogroup monoclonal antibodies (mAbs) were generated against the O:6 1, 6 2, 7 polysaccharide of Salmonella thompson. Five mAbs of either the O:6 1, or the O:6 2 specificities did not bind O:6,7,14 strains or LPS, showing that the O:6 determinant in these strains is neither O:6 1, nor O:6 2 . Thus antigenic conversion of O:6 2, 7 strains by phage 14 is accompanied by addition of O:14 as well as loss of O:6 2 Three mAbs which demonstrated group-wide reactivity, and were thus specific for O:7, recognized clearly separable epitopes hereby defined as sub-specificities, O:7 1 O:7 2 and O:7 3 Immunoblotting of mAbs against electrophoretically resolved LPS showed that factors O:6 1 and O:6 2 are expressed only in LPS molecules of high molecular mass whereas O:7 2 and O:7 3 are expressed only in relatively low-molecular-mass chains. These results are consistent with the expression of different antigenic determinants in structurally distinct subpopulations of O chains. The implication of the existence of distinct subpopulation of chains is that the published structure of the O:6,7 repeat unit is not fully representative of the O-antigenic structure of this group.