Immunochemistry of R Lipopolysaccharides of Escherichia coli

Abstract

Acapsular (K − ) forms were isolated from Escherichia coli strain E56b (serotype O8 :K27(A): H − ). A number of different R strains were obtained from the K − forms by selection of spontaneous mutants and by phage selection. The lipopolysaccharides of these R strains (consisting of core and lipid A) were subjected to mild acid degradation and, after removal of insoluble lipid A, the mixtures were fractionated by gel chromatography. Results of chemical analyses showed that the core oligosaccharides of different R mutants differed with respect to their sugar constituents as well as to the molar ratios of these constituents. A group of R mutants did not contain phosphate in their core oligosaccharides (P − mutants). Enzyme determinations indicated that one R mutant had a block involving UDP glucose pyrophosphorylase, whereas the enzymes of activation and interconversion of component sugars were intact in the other R mutants. By allelic exchange (mating with S‐form Hfr strains) it could be demonstrated that with one exception the chromosomal site of the SR mutation of all mutants maps close to mtl (mannitol utilization). In Salmonella the rfa locus maps in the same region. All R mutants had an unimpaired ( his ‐linked) rfb locus. The groups of mutants which differed in the sugar composition of their core oligosaccharides could also be differentiated serologically and by their sensitivity to phages. There was serological cross reactivity between the lipopolysaccharides of some R mutants with R mutants of Salmonella minnesota which also have a very incomplete core. It is concluded that the lipopolysaccharides of the R mutants described in this paper have incomplete core structures which result from blocks at successive stages in the synthesis of the coli R1 core. In analogy to Salmonella these E. coli R mutants should, with one exception, be termed rfa type mutants.