The effect of purified lipopolysaccharide on the bactericidal reaction of human serum complement.

Escherichia coli ML308 225 was killed and lysed by human serum. Bacterial sensitivity to serum was maximal for organisms in the early-exponential phase of batch culture and declined as growth proceeded. Bacterial killing was dependent upon the complete complement sequence and the subsequent action of serum lysozyme caused bacteriolysis. Purified lipopolysaccharide from this organism bound to serum-sensitive bacteria and inhibited the bactericidal reaction.