Morphological and biochemical characteristics were examined on four strains of the bacteria causative of “pseudotuberculosis” among yellowtail (Seriola quinqueradiata), and on a strain of Pasteurella piscicida, Janssen et Surgalla.
The observation that the pseudotuberculosis organisms were identical with P. piscicida was confirmed.
These organisms were all Gram-intermediate, non-motile rods. A peculiar morphological feature of the organisms is the transformation from rod-shaped cells in the early logarithmic growth phase to small coccoids or cocci in the stationary phase. The organisms gave positive Kovacs' oxidase reaction; fermented glucose in Hugh-Leifson's medium, and produced acid but no gas from a few other carbohydrates such as fructose, galactose, and mannose. They were sentistive to most of the antibiotics and antimicrobial drugs, including penicillin and polymyxin B; were halophilic; and did not grow at pH lower than 6.1.
Although the cells of these organisms did not show any typical coryneform appearance, nevertheless, the above characters suggest that they have a close relationship with coryneform bacteria and genus Arthrobacter seemed to be the most suitable genus to which they belong.