Characteristics of Vibriostatic Agent-Sensitive Aeromonas hydrophila Isolated from Ayu Plecogrossus altivelis and Its Pathogenicity

Abstract

From September to October in 1984, an epizootic occurred among cultured ayu Plecogrossus altivelis in Yamaguchi prefecture. The typical symptoms of the diseased ayu were congestion and swelling of anus, congestion of pectoral fin-base, subcutaneous hemorrhage of caudal peduncle. A bacterium was isolated from the kidney of all the diseased ayu. By infectivity trials the bacterium was proved to be pathogenic to ayu. The LD₅₀-value of an isolate to ayu was revealed 1.4×104 cells/g (b.w.) by intraperitoneal injection. These organisms were gram-negative, non-sporing rods with a single polar flagellum, and usually 0.7 to 0.8 by 0.8 to 3.0μm in size. On nutrient agar colonies developed within 24 hours at 25°C. The organisms grew at temperatures between 15 and 37°C. But no growth occurred 5°C ar 42°C. Growth occurred on SS agar, MacConkey agar and Aronson agar. The organisms gave positive oxidase and catalase reaction, utilized glucose, salicin and some carbohydrates fermentatively in Hugh-Leifson's medium and produce gas from many carbohydrates. IMViC reactions were (+(3/4), +, +, -), Hydrogen sulfide, 2, 3- butandiol dehydrase, elastase were produced. As a sole carbon source, L-arginine, L-histidine, L-glutamic acid, L-serine, saccharose, gluconate were utilized. The G+C content of the DNA was 62.0 mol% for a selected strain.
From the above-mentioned properties, the isolates should be identified as Aeromonas hydrophila, although the organisms are sensitive to the vibriostatic agent O/129.