Hemolysin Production by Beta-Hemolytic Streptococcus sp. Isolated from Yellowtail, Seriola quinqueradiata

Abstract

Hemolysin production by β-Streptococcus sp. isolated from yellowtail, Seriola quinqueradiata was investigated. The isolated strain was inoculated into Todd-Hewitt broth (THB) at pH 7.0 or 7.8, or into brain heart infusion broth (BHIB) at pH 7.0 or 7.4. After inoculation, the inocula were incubated at 25°C with shaking. Also the bacterium was cultured with THB and BHIB at pH 7.0 supplemented with 0.1, 1 or 10% (v/v) fetal calf serum (FCS), or with 0.001, 0.01 or 0.1% (w/v) bovine serum albumin (BSA) with the same conditions mentioned above. The growth of the bacterium was estimated by measurement of absorbance at 620 nm. The hemolytic activity against sheep erythrocytes of culture supernatant was assayed by measurement of hemoglobin absorption at 541 nm.
Hemolysin production was high, when the strain was cultured with THB at pH 7.0, and the maximum activity was found at 15 h after incubation, at late-logarithmic phase. In case of BHIB at pH 7.0, little hemolysin production was found. No hemolysin production was observed either with culture in THB at pH 7.8 or BHIB at pH 7.4. Using THB at pH 7.0, growth and hemolysin production was greatly increased by supplementation with 10% FCS, and was slightly increased by supplementation with 0.1% BSA.