A taxonomic study of the genus Haemophilus.

164 strains representing the genus Haemophilus, together with selected species of the genera Pasteurella and Actinobaeillus, have been subjected to taxonomic examination involving 141 physiological and biochemical tests. A numerical taxonomic analysis has separated the strains into twelve clusters. Four of the Haemophilus clusters contain sub-clusters which could not be clearly separated on the tests carried out. Six clusters contained the bulk of the Haemophilus strains with representative strains of H. aphrophilus forming a well separated species grouping close to the Pasteurella and Actinobacillus marker strains. The results of this study suggest that Haemophilus is a well separated genus based on -strains that require X,V or X and V for growth. The species H. influenzae is considered at present to be a single species, although there is a possibility that it contains several sub-species. Difficulties were found in separating the V-requiring strains into well differentiated species. In this work these strains were sub-divided into five species: H. parainfluenzae, H. parasuis, H. paragallinarum, H. somnus and the "H. avium complex". The H. parainfluenzae strains can be further sub-divided into haemolytic and non-haemolytic variants, but it is thought to represent a single species. The H. avium strains form a separate species. Close similarity between these strains and certain atypical H. parasuis and H. gallinarum strains was found and it is suggested that further work may reveal that they can be combined to form a single species. The H. paragallinarum and H. somnus strains, although closely associated, are considered to be separate species. An integral part of the work was to devise a suitable long term method for storing the bacteria. The broth cultures were successfully stored on glass beads at -80°C throughout this study, and the technique seems to have wide possibilities.