Cell Wall Ultrastructure of Strains of Haemophilus ducreyi and Haemophilus piscium

The Gram reactions and cell wall topographies of six strains of Haemophilus piscium, including the type strain, and four strains assigned to Haemophilus ducreyi were studied to elucidate the taxonomic position of the two species. All strains were predominantly gram negative when stained by the Gram method but showed differences in staining between individual cells. The six strains of H. piscium and one strain of H. ducreyi exhibited a cell wall of the gram-negative type, whereas the remaining three strains of H. ducreyi exhibited a cell wall structure typical of gram-positive microorganisms. The study thus confirms the classification of H. piscium as a gram-negative bacterium but indicates that the name H. ducreyi has been used for different groups of bacteria. Only one of the strains of H. ducreyi investigated can legitimately be assigned to the genus Haemophilus, and more information is required to settle the taxonomic position of the remaining three strains.