Characteristics and pathogenicity of a capsulated Pseudomonas isolated from goldfish

Characteristics of a capsulated bacterium isolated from an epizootic among goldfish (Carassius auratus) were determined as well as the ability of the bacterium to produce experimental infections. The bacterium was found to be a gram-negative rod which oxidized carbohydrates, produced green fluorescent pigment, and otherwise seemed to fit into the genus Pseudomonas, except that it was nonmotile and failed to oxidize gluconate. These last two characteristics are typical of pseudomonads. However, the bacterium was classified as a pseudomonad, best fitting the description of the nonmotile variety of Pseudomonas fluorescens. Goldfish and rainbow trout (Salmo gairdneri) were infected experimentally by injection, but not by being fed bacteria-laden food. Goldfish were infected by exposure to the bacterium, but only if two or three scales were removed prior to exposure. It is suggested that the bacterium is an opportunistic pathogen.