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

Ndubisi A. Nnalue^1,2,,3

Department of Medical Microbiology, Faculty of Medicine & Health Sciences, United Arab Emirates University, PO Box 17666, Al Ain, United Arab Emirates
Karolinska Institute, Department of Microbiology, Pathology and Infectious Diseases, Division of Clinical Bacteriology, Huddinge Hospital, S-14186, Huddinge, Sweden

³Author for correspondence: Ndubisi A. Nnalue. Tel: +1 913 588 7061. Fax: +1 913 588 1388.

ABSTRACT

The O-antigenic specificities found among salmonellae of serogroup C¹ 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:6² 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 6¹ 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:6² 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:6². 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:6² Three mAbs which demonstrated group-wide reactivity, and were thus specific for O:7, recognized clearly separable epitopes hereby defined as sub-specificities, O:7¹ O:7² and O:7³ Immunoblotting of mAbs against electrophoretically resolved LPS showed that factors O:6¹ and O:6² are expressed only in LPS molecules of high molecular mass whereas O:7² and O:7³ 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.

Present address: Department of Microbiology, Molecular Genetics & Immunology, University of Kansas Medical Center, 1000 Wahl Hall East, 3901 Rainbow Blvd. Kansas City, KS 66160-7382, USA.

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