Immunization of rainbow trout, Oncorhynchus mykiss (Walbaum), with a low molecular mass fraction isolated from Flavobacterium psychrophilum

Abstract

Flavobacterium psychrophilum, the causative agent of rainbow trout fry syndrome has become a widespread fish pathogen in freshwater aquaculture worldwide. In this study, a low molecular mass fraction (P25-33), with an approximate weight of 25-33 kDa, was identified among F. psychrophilum strains in an immunoblotting analysis with anti-F. psychrophilum sera. The immunogenic efficacy of the isolated and extracted P25-33 was investigated in two intraperitoneal immunization trials with rainbow trout, Oncorhynchus mykiss (Walbaum). The first trial included immunizations using P25-33 with Freund's complete adjuvant (FCA) and the second trial included immunizations using P25-33, formalin-inactivated whole and sonicated F. psychrophilum cell preparations without FCA. In both trials, antibody titres against F. psychrophilum were analysed with an enzyme-linked immunosorbent assay and the efficacy of the immunizations was determined by a challenge with F. psychrophilum. The P25-33 was shown to give rise to a protective immune response in rainbow trout after immunization with FCA, but not without FCA when a low concentration of P25-33 was used. Instead formalin-inactivated whole and sonicated cells of F. psychrophilum were able to protect the immunized fish more effectively when immunized without FCA. The results suggest that whole or sonicated F. psychrophilum cells could be better candidates for a cost-effective water-based injection vaccine than the immunogenic fraction.

Efficacy of a polyvalent injectable vaccine against Flavobacterium psychrophilum administered to rainbow trout (Oncorhynchus mykiss L.)

“…Previous studies using inactivated F. psychrophilum in conjunction with oil adjuvants have demonstrated protection, usually associated with increased levels of specific IgM in the serum of vaccinated fish (Fredriksen et al, 2013;Hoare, Jung, et al, 2017;Högfors, Pullinen, Madetoja, & Wiklund, 2008;Madetoja et al, 2006). The protection in the current study appears to be at least partly mediated by specific serum antibodies Previous studies have identified different molecular weight fractions (18-28, 41-49 and 70-100 kDa) as immunogenic molecules of F. psychrophilum by Western blotting, using convalescent rainbow trout serum (Crump, Perry, Clouthier, & Kay, 2001;Högfors et al, 2008;LaFrentz, Lindstrom, LaPatra, Call, & Cain, 2007).…”

“…Previous studies using inactivated F. psychrophilum in conjunction with oil adjuvants have demonstrated protection, usually associated with increased levels of specific IgM in the serum of vaccinated fish (Fredriksen et al., ; Hoare, Jung, et al., ; Hoare, Ngo, et al., ; Högfors, Pullinen, Madetoja, & Wiklund, ; Madetoja et al., ). The protection in the current study appears to be at least partly mediated by specific serum antibodies (IgM) as shown by ELISA, agglutination and Western blotting.…”

“…Previous studies have identified different molecular weight fractions (18–28, 41–49 and 70–100 kDa) as immunogenic molecules of F. psychrophilum by Western blotting, using convalescent rainbow trout serum (Crump, Perry, Clouthier, & Kay, ; Högfors et al., ; LaFrentz, Lindstrom, LaPatra, Call, & Cain, ). These proteins have potential to be the basis for a recombinant vaccine to provide cross‐protection against F. psychrophilum .…”

Immersion exposure of rainbow trout (Oncorhynchus mykiss) fry to wildtype Flavobacterium psychrophilum induces no mortality, but protects against later intraperitoneal challenge

“…The growth phase of the bacterial challenge culture could also affect the virulence [4] as could the number of passages on artificial medium (authors' own observation). Challenge by intraperitoneal, subcutaneous or intramuscular injection [2,5,7] fish, including the protective immune mechanisms of the skin and may therefore not be appropriate for evaluation of immersion vaccines [7,13]. To address this matter, the present study aimed at investigating whether immersion in high titres of wildtype isolates of F. psychrophilum would be able to stimulate a systemic immune response conferring protection against a subsequent ip challenge.…”

“…Vaccination by intraperitoneal (ip) injection of heat inactivated, formalin killed, or sonicated cells or subunit vaccines, with or without use of adjuvant, may confer good protection [1,2,5,8], but ip vaccination is not realistic for small fry. The fry have to be vaccinated as early as possible, as RTFS can cause problems soon after start of feeding, when the fish are only around 0.2e0.5 g. For salmonids, the minimum size of onset of an economically acceptable level of adaptive immunity is from 0.5 to 2.5 g by use of inactivated bacterial immersion vaccines of Yersinia ruckeri and Vibrio anguillarum [9e11].…”