Dissociation of virulence and protection from infection by mutant analysis in Haemophilus influenzae type b.

A Haemophilus influenzae type b (Hib) outer membrane protein with an apparent molecular weight of 98,000 (98K) previously has been shown to react with antibodies that protect against experimental Hib disease. A mutant lacking the ability to synthesize this 98K protein was produced by chemical mutagenesis and identified in a colony blot-radioimmunoassay by its failure to react with a 98K protein-specific monoclonal antibody. DNA from this mutant was used to produce a 98K protein-negative transformant of the wild-type parental strain. Comparison of the relative degree of virulence of the parental strain and the 98K protein-negative transformant in an animal model system revealed no differences in the abilities of these two strains to produce bacteremia after intranasal challenge. These results indicate that the Hib surface-exposed 98K outer membrane protein that reacts with protective antibodies plays no detectable role in the expression of virulence by Hib in an animal model system.