The bacterium Salmonella Uccle belongs to serotype O:54 in the Kauffmann'a-White scheme. Group O:54 is unique among the serogroups belonging to the genus Salmonella. Normally, the enzymes involved in the biosynthesis of the repeating units of somatic antigen are encoded by a set of genes, located in the region of the bacterial chromosome. Expression of O54 factor is associated with the presence of the plasmid. Factor O54 can be lost spontaneously in the subcultures of some serotypes. In these cases, the O54 negative variants become indistinguishable from the serotypes classified in other groups. We noticed lower activity of LPS-u O:3,54 with rabbit sera against antigens O:3, when compared with the activity of sera anti-A:54, which may indicate a partial inhibition of the expression of factor O:3 on the surface of the bacterial cell. The main aim of our study was to answer the question whether the products of different biosynthetic pathways combine on the outer side of the cytoplasmic membrane, thus forming a single chain or separate chains. Therefore, the O-polysaccharides (O-antigen) of Salmonella Uccle O:3,54 were isolated by mild acid degradation of both obtained LPSs and their structure was established using sugar and methylation analysis and NMR spectroscopy. The primary structure of two separate O-polysaccharide chains isolated from Salmonella Uccle were established. (C) 2013 Elsevier Inc. All rights reserved.