Numerical taxonomy of Haemophilus.

A numerical taxonomic study of strains of Haemophilus, together with representatives of Pasteurella and Actinobacillus, showed 12 reasonably distinct phenons. These phenons corresponded in the main with recognized species. Phenon 1 contained H. influenzae and H. aegyptius, and phenon 2 represented H. parasuis. Phenon 3 comprised haemolytic V-requiring strains similar to H. parahaemolyticus. Phenons 4 and 5 were very similar, and comprised a number of V-requiring strains including H. parainfluenzae and H. paraphrophilus. Phenon 6 contained H. avium and a few other strains from fowls or swine. Phenon 8 represented H. paragallinarum and H. somnus, and phenon 9 contained H. aphrophilus strains. Phenons 7, 10 and 11 contained strains of Pasteurella and Actinobacillus, and strains of H. piscium were recovered in phenon 12. The last appeared not to belong to the genus Haemophilus. A small proportion of strains were unclustered. Although the groupings were broadly satisfactory, they were not as sharply demarcated as phenons in comparable taxonomic studies, and the reasons for this are discussed.