넙치, Paralichthys olivaceus 병어에서 분리된 Streptococcus parauberis의 특성

Abstract

Streptococcal diseases are serious problems in fresh water and marine fish culture industry worldwide. In recent years, the importance of infection caused by Streptococcus parauberis has increased since severe outbreaks in cultured olive flounder (Paralichthys olivaceus) were recorded in Korea. The aims of the present study were to investigate phenotypic characteristics of S. parauberis, and pathogenic and immunological characteristics between S. parauberis and S. iniae. In this study, S. parauberis isolated from infected olive flounder was identified by biochemical and genotypic characteristics and was investigated the characteristics of morphological, physiological, protein profile and enzyme activity of ECP. Immune responses of the fish to the pathogen was characterized by bactericidal activity in the serum, phagocytic activity and reactive oxygen intermediaters (ROIs) production of olive flounder. S. parauberis strains used in this study were overall very similar on the basis of biochemical characteristics. S. parauberis appeared α or γ hemolytic activity whereas S. iniae showed β hemolytic activity. A multiplex PCR-based method using 4 different primer sets was performed for rapid detection of various Gram-positive cocci fish pathogens, i.e. Lactococcus garviae, S. iniae and S. parauberis. The protein profiles of formalin killed cells of S. parauberis presented two major bands around 47 KDa, and overall the profiles were very similar to the reference strain. The optimum temperature and salinity for the growth of strains were 27 ℃ and 0 % NaCl, and they did not grow at 45 ℃ and 10 % NaCl, respectively. The capsule of both S. parauberis and S. iniae seems to be associated with the ability to resist killing by normal sera. Also, capsulated strains could survive in phagocytes and induce low ROIs production.