Bacteriophage attachment sites, serological specificity, and chemical composition of the lipopolysaccharides of semirough and rough mutants of Salmonella typhimurium

Extracted lipopolysaccharides (LPS) from one smooth, one semirough, and five rough mutants of Salmonella typhimurium LT2 or LT7, for which the chemical structure of the polysaccharide chain had been elucidated by using methylation analysis, were characterized with passive hemagglutination inhibition and phage inactivation experiments. Each addition of a sugar residue to a LPS from chemotype Rc was reflected in changed serological reactivity and phage-inhibiting activity of a collection of bacteriophages of the isolated LPS. Thus, certain criteria can be established for a classification of rough mutants of S. typhimurium. The observation that the serological RII specificity corresponds to a completed common core polysaccharide was verified. The serological RI specificity was found in LPS with terminal d-galactose I residues. One of the mutants, SL733, yielded a LPS which cross-reacted with anti-O5 factor serum although the polysaccharide was virtually free from contaminating O-specific material. The O5 reactivity was destroyed by alkaline treatment of SL733 LPS. The smooth- and rough-specific Felix O-l (FO) and the rough-specific 6SR and Br2 phages were shown to have their receptors in the LPS. There was a good correlation between the adsorption rate constant to whole cells and the phage inhibiting activity of isolated LPS suggesting that the LPS exert the major influence on the attachment of these phages to the bacteria. The polysaccharide structures in the LPS necessary for attachment of the 6SR and Br2 phages were defined. It was found that measuring the phage-inhibiting properties of isolated LPS as PhI(50) (LPS concentration required to inactivate 50% of the phages under defined conditions) was a more sensitive method for a characterization of the LPS than the serological and chemical assays used.