The aim of the present study was to analyse the importance for non-typeable Haemophilus influenzae (NTHi) isolated from patients with sepsis (invasive isolates) compared to nasopharyngeal isolates from patients with upper respiratory tract infection to resist the complement-mediated attack in human serum and to correlate this to disease severity. We in detail studied and characterized cases of invasive NTHi disease. All patients with invasive NTHi isolates were adults and 35 % had a clinical presentation of severe sepsis according to the ACCP/SCCM classification of sepsis grading. Moreover, 41 % of the cases had evidence of immune deficiency. The different isolates were analyzed for survival in human serum, for binding of [(125)I]-labeled purified human complement inhibitors C4b-binding protein (C4BP), Factor H and vitronectin in addition to binding of regulators directly from serum. No significant differences were found when blood and nasopharyngeal isolates were compared, suggesting that interactions with the complement system are equally important for NTHi strains irrespectively of isolation site. Interestingly, a correlation between serum resistance and invasive disease severity was found. The ability to resist the attack of the complement system seems to be important for NTHi strains infecting the respiratory tract as well as the blood stream.
- Microbiology in the medical area