Genetic and immunochemical studies on Escherichia coli O14:K7:H-.

Abstract

Acapsular (K−) mutants selected from Escherichia coli O14:K7 proved to be rough (R) forms, indicating the absence of O-specific polysaccharides in the wild type K+ strain. This suggestion was confirmed by chemical analysis and degradation studies of the lipopolysaccharides from K+ and K− strains. In order to determine the chromosomal site of the S/R mutation in E. coli O14:K7, recombination experiments were performed. An acapsular R form (F2513) of E. coli O14:K7 was crossed with the E. coli O8 donor Hfr59. Most of the recombinants selected for the donor his+ allele showed O8-specificity in consequence of the transfer of the his-linked donor rfb cluster, governing the synthesis of O8-specific polysaccharides. This indicates that the rough phenotype of E. coli O14 is caused by mutational defects in the rfb genes and that this R strain produces a complete lipopolysaccharide core structure. As shown by serological tests and phage typing the E. coli O14 lipopolysaccharide core is different from other known complete core types (R1–R3 and K12). Partial cross reactivity between the lipopolysaccharides of E. coli O14 and E. coli R1 mutants indicates a certain degree of structural similarity of the respective cores. Glucose, galactose, heptose and 2-keto-3-deoxy-octonate were identified as constituents of both core oligosaccharides. Quantitative analysis, however, revealed differences in the molar ratios of galactose : glucose : heptose which in the core of E. coli O14 is 3:2:3 and in the R1 core is 2:3:3. The results described here showed that E. coli O14:K7 lacks O-specific polysaccharides and represents an encapsulated rough (R) strain with a complete lipopolysaccharide core designated as R4.