Identification of haemolytic Haemophilus species isolated from human clinical specimens and description of Haemophilus sputorum sp. nov

Abstract

Haemolytic Haemophilus strains with no requirement for X factor are regularly isolated from sputum and throat swabs and occasionally from invasive infections, but the classification of such strains is not clear. We characterized 56 strains with a phenotype concordant with Haemophilus parahaemolyticus (V, but not X factor-dependent; urease-positive; tryptophanase-negative; ornithine decarboxylase-negative) by extended phenotypic testing and 16S rRNA gene sequencing. In addition, 31 of the strains and representative type strains were investigated by multilocus sequence analysis based on 3 housekeeping gene fragments. Most strains could be assigned to H. parahaemolyticus and were characterized by expression of IgA1 protease and a negative test for β-galactosidase. Isolation of H. parahaemolyticus from various infections and its absence among more than 300 commensal Haemophilus isolates suggests a pathogenic potential of this organism. The majority of haemolytic strains with β-galactosidase activity did not cluster with the type strain of H. paraphrohaemolyticus, but constituted a distinct and coherent novel taxon. Ten strains of this new taxon proved to be genetically and phenotypically homogeneous. Few biochemical characters discriminate the new taxon from related Haemophilus species, but identification is easily accomplished by routine matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Genetic, biochemical, and spectrometry data show that the taxon merits recognition as a novel species of Haemophilus. The name Haemophilus sputorum is proposed, with CCUG 13788(T) (=DSM 24472(T)=NCTC 13537(T)) as the type strain.