Role of Lipopolysaccharide and Capsule in the Serum Resistance of Bacteremic Strains of 'Escherichia coli'

摘要

To define the relative roles of capsule and lipopolysaccharide in the virulence of Escherichia coli obtained from blood, the authors compared the behavior of K1-and K5-encapsulated strains in serum bactericidal and rat virulence assays. Unencapsulated isogenic mutants selected from five parents strains of E. coli 012:K1, but not of 018:K1 or 07:K1 (all rough-specific phage insensitive), were lysed by normal human sera. In contrast, isogenic mutants from strains. There was a difference in LD50 median lethal dose (radiation) in newborn rats between K1-positive and K1-negative pairs of E. c oli serotypes 018 and 07 and a difference between isogenic pairs of serotypes, however, required the K5 capsule for serum resistance. The authors conclude that some O serotypes require encapsuluation for optimal virulence but that other O serotypes may not. (Reprints).