A pivotal role for the Streptococcus iniae extracellular polysaccharide in triggering proinflammatory cytokines transcription and inducing death in rainbow trout


  • Editor: Jeff Cole

Correspondence: Avi Eldar, Department of Poultry and Fish Diseases, The Kimron Veterinary Institute, PO Box 12, Bet Dagan 50250, Israel. Tel.: +972 3 968 1760; fax: +972 3 968 1739; e-mail: eldar@agri.huji.ac.il


Streptococcus iniae is a major pathogen of fish, causing considerable economic losses in Israel, the United States and the Far East. Containment of mortalities through vaccination was recently compromised due to the emergence of novel vaccine-escape strains that are distinguished from previous strains by their ability to produce large amounts of extracellular polysaccharide (EPS) that is released to the medium. In vitro and in vivo data now indicate that the EPS is a major virulence factor, capable of triggering the proinflammatory cytokine machinery and inducing mortality of fish. Streptococcus iniae EPS might therefore be considered to be responsible for sepsis and death just as lipopolysaccharide is for Gram-negative pathogens.