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The Brazilian purpuric fever (BPF) clone of Haemophilus influenzae biogroup aegyptius causes a fatal septicaemic disease, resembling fulminant meningococcal sepsis, in children. When isolate F3031 was grown under iron-limiting conditions, the presence of several iron-regulated proteins of 38-110 kDa was revealed by electrophoretic analysis and a Fur homologue was shown by immunoblotting. Dot-blot assays and immunoblotting indicated that BPF cells bound human transferrin and contained transferrin-binding proteins in the outer membrane. However, the binding activity and the biosynthesis of these proteins were detected even under iron-rich conditions. Immunoblot analysis demonstrated the presence of a periplasmic protein related to the ferric iron-binding protein A (FbpA), the major iron-binding protein described in Neisseria spp. However, the FbpA homologue in strain F3031 was constitutively expressed and was smaller than the periplasmic protein detected in H. influenzae type b strain Eagan. The periplasm of strain F3031 also contained a protein related to the Streptococcus parasanguis FimA protein which recently has been shown to be involved in iron acquisition in Yersinia pestis. Although the Eagan and F3031 FimA homologues had a similar mol. wt, of 31 kDa, the expression of the BPF fimA-like gene was not regulated by the iron concentration of the culture medium.