title: The effect of serum-factor induced resistance to somatic antibodies on the virulence of Haemophilus influenzae type b.
abstract: Studies on the pathogenesis of Haemophilus influenzae b infection have used bacteria grown in vitro which are relatively serum-sensitive (using serum devoid of anticapsular antibody) compared to organisms taken from infected hosts. We compared the virulence of relatively serum-sensitive and serum-factor induced serum-resistant H. influenzae b by inoculating rats with organisms having one or the other phenotype. The serum-resistant phenotype was more virulent following intraperitoneal or intravenous inoculation; however, there was no difference in the incidence of colonization or bacteraemia following intranasal inoculation. Furthermore, organisms colonizing the pharynx of rats had the serum-resistant phenotype. Thus, different phenotypes of the same strain of H. influenzae b differed in virulence following parenteral, but not intranasal, inoculation of bacteria. This could be explained by a change from serum-sensitive to serum-resistant phenotype shortly after entering the nasopharynx. The phenotype of micro-organisms grown in vitro may differ from organisms in infected individuals and these differences may be of critical importance in studies of immunity to infection and the pathogenesis of infection.
mesh_terms: D000818:Animals; D000906:Antibodies; D001770:Blood Bactericidal Activity; D006193:Haemophilus influenzae / Q000235:genetics / Q000472:pathogenicity*; D009305:Nasopharynx / Q000382:microbiology; D010641:Phenotype; D051381:Rats; D014774:Virulence
chemical_list: D000906:Antibodies