title: The type b capsular polysaccharide as a virulence determinant of Haemophilus influenzae: studies using clinical isolates and laboratory transformants.
abstract: Haemophilus influenzae organisms elaborating one of six capsular polysaccharides (types a-f) colonize the respiratory tract of humans, but only type b strains commonly cause systemic infections. To investigate the role of capsular polysaccharides as virulence determinants, rats were inoculated with capsulated (types a-f) or noncapsulated clinical isolates or with laboratory-derived type b and type d transformants of a noncapsulated strain. After intraperitoneal inoculation, all capsulated strains possessed the potential for systemic infection, but type b strains were more virulent; noncapsulated strains were noninvasive. After intranasal inoculation, only type b strains were invasive. There was no difference in efficiency of nasopharyngeal colonization between type b and type d transformants. After intravenous inoculation, only type b strains resulted in persistent bacteremia. Thus, type b strains--clinical isolates or transformants--display unique virulence characteristics. These data suggest that elaboration of type b capsule is necessary and sufficient for this virulence of H. influenzae type b in the rat.
mesh_terms: D000281:Administration, Intranasal; D000818:Animals; D001775:Blood Circulation; D006192:Haemophilus Infections / Q000209:etiology*; D006193:Haemophilus influenzae / Q000235:genetics* / Q000472:pathogenicity; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D011135:Polysaccharides, Bacterial; D051381:Rats; D014169:Transformation, Bacterial; D014774:Virulence
chemical_list: D011135:Polysaccharides, Bacterial