Binding of Heme-Hemopexin Complexes by Soluble HxuA Protein Allows Utilization of This Complexed Heme byHaemophilus influenzae

ABSTRACT Utilization of heme-hemopexin as a source of heme byHaemophilus influenzae type b is dependent on expression by this bacterium of the 100-kDa HxuA protein, which is both present on the bacterial cell surface and released into the culture supernatant (L. D. Cope, R. Yogev, U. Muller-Eberhard, and E. J. Hansen, J. Bacteriol. 177:2644–2653, 1995). Radioimmunoprecipitation analysis showed that the soluble HxuA protein present in H. influenzae type b culture supernatant bound heme-hemopexin complexes in solution. An isogenic H. influenzae type bhxuA mutant was unable to utilize soluble heme-hemopexin complexes for growth in vitro unless soluble HxuA protein was provided exogenously. Soluble HxuA protein secreted by a nontypeableH. influenzae strain also allowed growth of thisH. influenzae type b hxuA mutant. These results indicated that the heme present in heme-hemopexin complexes is rendered accessible to H. influenzae when these complexes are bound by the soluble HxuA protein.

Clinical Features Fail to Distinguish Respiratory Infections Caused byBranhamella catarrhalisfrom Those Caused byHaemophilus Influenzae

Branhamella catarrhalisis being isolated with increasing frequency from patients with symptoms and signs of respiratory tract infection. Records of 77 patients were reviewed to define the spectrum of respiratory illness and to compare clinical and laboratory features with those of respiratory infection due toHaemophilus influenzae.BothB catarrhalisandH influenzaecaused respiratory infection predominantly in elderly males with underlying heart or lung disease. There were no clinical or laboratory features aside from sputum Gram stain and culture which differentiated the two groups. Although fewer than one-half of each group received antibiotics, no patient developed progressive respiratory disease.