Vaccine efficacy in spotted wolffish Anarhichas minor: relationship to molecular variation in A-layer protein of atypical Aeromonas salmoncida

Abstract

Atypical Aeromonas salmonicida strains comprise a heterogeneous group in terms of molecular and phenotypic characteristics. They cause various conditions of ulcer diseases or atypical furunculosis and are being isolated in increasing number from various fish species and geographical areas. Several marine fish species susceptible to atypical A. salmonicida, including spotted wolffish Anarhichas minor O., are now being farmed and new vaccines may be needed. A commercial furunculosis vaccine for salmon is reported to protect wolffish poorly against experimental challenge with atypical A. salmonicida. The protective antigen(s) in furunculosis vaccines is still unclear, but in oiladjuvanted vaccine for Atlantic salmon Salmo salar L., the surface A-layer was shown to be important for protection. In spotted wolffish, the efficacy of atypical furunculosis vaccines seems to vary with the atypical A. salmonicida strains used as bacterin in the vaccine. In the present study we investigated whether differences in the A-layer protein among atypical strains might be responsible for the observed variation in vaccine efficacy. Atypical A. salmonicida strains from 16 fish species in 11 countries were compared by genome polymorphism analysis using amplified fragment length polymorphism (AFLP) fingerprinting and by comparative sequencing of the vapA genes encoding the A-protein. The A-protein sequences appeared to be highly conserved except for a variable region between Residues 90 to 170. Surprisingly, the grouping of strains based on AFLP-or A-protein sequence similarities was consistent. In addition, serological differences in the A-protein among the strains were demonstrated by an A-protein-specific monoclonal antibody. Vaccines based on atypical A. salmonicida strains possessing genetically and serologically different A-layer proteins were shown to result in significantly different protection in spotted wolffish. KEY WORDS: Atypical Aeromonas salmonicida · Amplified fragment length polymorphism · AFLP · A-layer protein · Vaccine · Spotted wolffish Resale or republication not permitted without written consent of the publisherDis Aquat Org 56: [31][32][33][34][35][36][37][38][39][40][41][42] 2003 (PFGE) (Umelo & Trust 1998, O'hIci et al. 2000 and amplified fragment length polymorphism analysis (AFLP) (Lund et al. 2002a) have been used to demonstrate genetic diversity among the atypical strains. However, these methods are not comparable (Austin et al. 1998), and a reliable method for classification of atypical strains is still lacking.Several marine fish species susceptible to atypical Aeromonas salmonicida infection are now being farmed, and vaccine development will be necessary. It is not known if species-specific vaccines are needed, or if vaccines that protect against all genotypes of atypical A. salmonicida in various fish species can be developed. For the past 10 yr furunculosis in Atlantic salmon Salmo salar L. has been successfully controlled by the use of highly efficient oil-adjuvanted vaccines. Commercia...

Genetic diversity among A-proteins of atypical strains of Aeromonas salmonicida

“…salmonicida strain has been sequenced and the deduced A-protein sequence consists of 502 amino acids including a 21 amino acid signal peptide (Chu et al 1991; GenBank accession number M64655). The A-proteins of 4 atypical strains of A. salmonicida were shown to have a sequence similarity of 90 to 94% compared to the typical reference sequence M64655 (Lund et al 2003b). Most of the A-protein sequence is highly conserved, apart from a region between residues 90 and 180.…”

“…Also, vaccines based on atypical Aeromonas salmonicida strains from the 3 different clusters shown in Fig. 2 showed significant differences in protection of spotted wolffish when challenged with strain 4067 (Lund et al 2003b). Today, atypical furunculosis in farmed marine fish species is an increasing problem.…”

“…This is supported by the fact that although a polyclonal antiserum raised against a typical A. salmonicida strain and adsorbed with atypical strains resulted in a great reduction of the titre, significant reactivity remained, indicating antigenic differences between the atypical and typical strains (Doig et al 1993). Further, an A-protein-specific monoclonal antibody was shown to react with a restricted number of atypical strains of A. salmonicida (Lund et al 2003b). However, as demonstrated in our A-protein sequences, the C-terminal region appears to be very conserved as 8 different monoclonal antibodies specific to this region of the A-protein reacted with all 25 typical and atypical strains of A. salmonicida studied (Doig et al 1993).…”

“…The A-protein sequences were deduced from the vapA gene sequences obtained by primer walking of 1565 bp PCR-products as described by Lund et al (2003b). The nucleotide sequences of 15 vapA genes representing A-protein diversity have accession numbers from AJ749879 to AJ749893.…”

Atypical furunculosis vaccines for Atlantic cod Gadhus morhua: impact of reattached Aeromonas salmonicida A-layer protein on vaccine efficacy

“…The Asa 4075 is O-chain negative and therefore secretes the A-protein to the culture medium. The vapA gene has been shown to possess a variable region that can be used for grouping of atypical isolates (Lund et al 2003b). The strains aAs 4099 (GenBank accession number AJ749879), Asa 4036 (AJ49888) and Asa 4075 all group together (Lund & Mikkelsen 2004, authors' unpubl.…”