Vaccination of rainbow trout, Oncorhynchus mykiss (Walbaum), with recombinant and DNA vaccines produced to Flavobacterium psychrophilum heat shock proteins 60 and 70

Abstract

Flavobacterium psychrophilum heat shock proteins (Hsp) 60 and 70 are highly immunogenic and were therefore investigated as potential vaccine candidates. Recombinant Hsps were purified from Escherichia coli and rainbow trout (Oncorhynchus mykiss) were intraperitoneally injected with phosphate buffered saline/Freunds complete adjuvant (FCA), 8 microg of rHsp60/FCA, rHsp70/FCA or a combination of 4 microg each of rHsp60 and rHsp70/FCA. Antibody responses against recombinant Hsp60 and Hsp70 8 weeks post-immunization were observed, but only fish immunized with rHsp70 exhibited highly elevated antibody levels against F. psychrophilum whole cell lysate. Some cross reactivity occurred, which may have been due to the V5 tag common to both proteins. Protection against F. psychrophilum challenge was not observed in any treatments at 8 weeks post-immunization. To further investigate any protective effect of these proteins, hsps were polymerase chain reaction amplified and cloned into pVAX1. Rainbow trout were intramuscularly injected with 8 microg of pVAX1hsp60, pVAX1hsp70 or a combination of 4 microg each of pVAX1hsp60 and pVAX1hsp70. Antibody responses at 4 weeks post-immunization were low and protection was not observed following challenge at 6 or 10 weeks post-immunization. Although Hsps of F. psychrophilum have been shown to be immunodominant, these antigens do not appear to be good vaccine candidates when delivered alone or in combination.

Bacterial coldwater disease of fishes caused by Flavobacterium psychrophilum

“…Mean mortality in the heat shock protein treatment groups was 74% or greater and significant protection compared to control groups was not afforded to the fish. Plant et al [43] concluded that these proteins did not seem to be useful for further vaccine development. LaFrentz et al [130] identified and analyzed specific proteins of F. psychrophilum cultures grown in vivo and in vitro in an iron-limited medium.…”

“…Aoki et al [41] showed that 18 and 24 h F. psychrophilum cultures with challenge doses of 2.00 · 10 7 and 8.50 · 10 7 cfu/mL, respectively, resulted in significantly greater mortalities than was obtained with a 48 h culture, even though the 48 h culture had a greater number of cells (3.40 · 10 8 cfu/mL). Injection challenge methods are often used to expose experimental groups of fish to F. psychrophilum [36,[42][43][44]. Decostere et al [42] noted that only 10-week old rainbow trout developed clinical signs and mortality following IP injections with 1.00 · 10 6 cfu, while fish 5 or 15 months old did not.…”

“…Plant et al [43] demonstrated high antibody responses in rainbow trout to heat shock proteins 60 and 70, singularly or in combination, which were administered (IP) with Freunds complete adjuvant. Eight weeks post-immunization, the fish were exposed to 5.0 · 10 6 or 1.25 · 10 7 cfu F. psychrophilum by subcutaneous injections.…”

Flavobacterium psychrophilum vaccine development: a difficult task

“…These cellular proteins were expressed in both virulent and non‐virulent strains of F. psychrophilum and were highly reactive against trout antiserum, indicating that they were indeed immunodominant antigens of the bacteria. However, Plant and colleagues () showed, in an experimental challenge, that vaccination of rainbow trout by recombinant and DNA vaccines based on these proteins resulted in no protection against F. psychrophilum .…”

Diversity of Flavobacterium psychrophilum and the potential use of its phages for protection against bacterial cold water disease in salmonids

“…Despite the substantial economic losses that F. psychrophilum causes in freshwater aquaculture, a specific vaccine is currently unavailable (Plant, Lapatra & Cain 2009) and antibiotics are the only treatment (Nematollahi et al. 2003).…”