Genetic and phenotypic variation in the capsulation and virulence of culture collection strains of Haemophilus influenzae type b.

Haemophilus influenzae type b strains deposited in the National Reference Collections of the United States, United Kingdom and Sweden are derived from strains isolated in the United States during the 1940s. With respect to both the genetic locus for capsulation and to virulence, assessed in the infant rat bacteremia model, these strains are no longer representative of clinical isolates which currently cause meningitis and other serious infections in children all over the world. Alternative well-characterized strains resembling current common clinical isolates may often be more suitable for the study of Haemophilus influenzae pathogenicity.