Non-hemolytic Streptococcus Isolated from the Brain of the Vertebral Deformed Yellowtail

Abstract

Two species of streptococci were isolated from the brain of the vertebral deformed yellowtail cultured in Lake Hamana, Shizuoka Prefecture. One species was α-hemolytic and the other was non-hemolytic. The α-hemolytic isolates were identified as the well-known etiological agent of streptococcicosis in yellowtail.
The non-hemolytic Streptococcus did not grow in media containing 0.1 % methylene blue milk, 6.5 % NaCl, 10% and 40% bile. Growth at pH 9.6 was positive, but growth at 10°C and 45°C, and heat tolerance (60°C for 30 min) were negative. Final pH in glucose broth was 4.5. The isolate did not hydrolyze gelatin, starch, esculin and arginine, but hydrolyzed sodium hippurate. This non-hemolytic Streptococcus was not classified as any of Lancefield's serological groups. This Streptococcus was placed in the Streptococcus group I, B because growth at 10°C and 45°C were negative and hydrolysis of sodium hippurate was positive. The bacterium, however, was not identical in biochemical characteristics with any formerly established species of the genus Streptococcus.
The non-hemolytic Streptococcus showed fatal pathogenicity for yellowtail by intraperitoneal injection. Further work is required to explain between the isolate and the vertebral deformity.