The phylogeny of human isolates of Haemophilus species was estimated based on partial sequences of four separate housekeeping genes. The clustering of each set of sequences was in accordance with speciation of the strains with few exceptions: of 108 gene fragments examined, only three appeared to have been subject to recombination events across the species barrier. Housekeeping gene similarity supported previous DNA-DNA hybridization data for the genus rather than the phylogeny inferred from 16S rRNA gene sequence comparison. The similarity of sequences of Haemophilus parainfluenzae with those of Haemophilus influenzae suggested preservation of the former species in the genus Haemophilus. Three strains representing a novel taxon were unique with respect to the four investigated gene loci. 16S rRNA gene sequence analysis suggested that this taxon belonged to the Parainfluenzae cluster. DNA-DNA hybridization data supported this generic placement. Nine strains of the novel taxon were available for analysis. They were distinct from representatives of all current species of the genus Haemophilus by conventional phenotypic characterization. Genotypic and phenotypic data show that the strains merit recognition as a novel species of Haemophilus. The name Haemophilus pittmaniae sp. nov. is proposed, with HK 85T (=CCUG 48703T=NCTC 13334T) as the type strain.
