ARS | Publication request: Immunization of rainbow trout Oncorhynchus mykiss (Walbaum) with a crude lipopolysaccharide extract from Flavobacterium psychrophilum

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2012
Publication Date: N/A

Interpretive Summary: Flavobacterium psychrophilum is an economically important bacterial pathogen of salmonid aquaculture worldwide. Control methods are limited and oftentimes ineffective; hence, research efforts have focused on vaccine development. Lipopolysaccharide (LPS) is a carbohydrate that is found on the outer surface of some bacterial pathogens. Research on F. psychrophilum has suggested that this carbohydrate may be important for eliciting protective immune responses. In this study, we tested this by immunizing rainbow trout with crude LPS extracted from the bacterium. Following immunization, fish were infected with the bacterium to determine if immunization with the LPS has an effect on survival. The results demonstrated that immunized fish did not generate specific immune responses against the LPS and only minimal levels of protection were conferred. The results indicate that higher immunization doses may be necessary to elicit specific immune responses against the LPS and other bacterial components may be more important for protective immunity against F. psychrophilum.

Technical Abstract: Control methods for Flavobacterium psychrophilum, the etiologic agent of bacterial coldwater disease (CWD) and rainbow trout fry syndrome, are limited and oftentimes ineffective; hence, research efforts have focused on vaccine development. This study tested the hypothesis that a crude lipopolysaccharide (LPS) extract from F. psychrophilum will elicit a protective immune response in rainbow trout Oncorhynchus mykiss (Walbaum) against F. psychrophilum challenge. Rainbow trout (mean weight, 3 g) were immunized intraperitoneally with the following treatment and control preparations: 10 µg of crude LPS with or without Freund’s complete adjuvant (FCA), 25 µg of crude LPS with or without FCA, and saline with or without FCA. Immunization of fish with 10 or 25 µg of crude LPS/FCA resulted in significant antibody responses against F. psychrophilum by ELISA using a whole-cell lysate as the coating antigen, but only minimal levels of protection were conferred following F. psychrophilum challenge at 14 weeks post-immunization. Western blot analyses demonstrated that fish exhibited antibodies specific for low molecular mass proteins present in the crude LPS extract, but did not exhibit antibodies specific for F. psychrophilum LPS. The results indicate that higher immunization doses and/or a more purified LPS extract may be necessary to elicit specific antibody responses against F. psychrophilum LPS.