The Aeromonas salmonicida A-layer protein is an important protective antigen in oil-adjuvanted vaccines

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...

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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

Lund¹,

Espelid²,

Mikkelsen³

2003

“…Our interest in the surface A-layer is related to its possible role as a protective antigen in furunculosis vaccines. In oil-adjuvanted furunculosis vaccines for salmon, the A-layer appeared to be important, since vaccines containing strains without A-layer did not provide any protection (Lund et al 2003a). Also, vaccines based on atypical Aeromonas salmonicida strains from the 3 different clusters shown in Fig.…”

mentioning

confidence: 99%

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

Lund¹,

Mikkelsen²

2004

The virulence array protein gene A (vapA) encoding the A-protein subunit of the surface layer of 23 typical and atypical strains of Aeromonas salmonicida from salmonids and marine fish species were sequenced, and the deduced A-protein sequences compared. The A-proteins of the typical A. salmonicida ssp. salmonicida strains were shown to be identical, while amino acid variability was revealed among A-proteins of atypical strains. The highest amino acid variability appears to be in a predicted surface exposed region and is believed to result in antigenic differences among the atypical strains of A. salmonicida. KEY WORDS: Atypical Aeromonas salmonicida · A-protein sequence · Surface A-layerResale or republication not permitted without written consent of the publisher

Section: Resale or Republication Not Permitted Without Written Consenmentioning

confidence: 99%

“…Earlier studies have shown that A-layer-possessing Aeromonas salmonicida used in oil-adjuvanted vaccines elicit acceptable protection against homologous challenge in salmon, as well as in marine fish species. However, vaccines based on A-layer-deficient isolates failed to protect in salmon and protected poorly or not at all in cod and Atlantic halibut Hippoglossus hippoglossus (Lund et al 2003a,b, Mikkelsen et al 2004, Lund et al 2008a.Various A-layer functions have been identified by using A-layer-deficient mutants. In addition, physical reconstitution of the A-layer proved to be a useful tool in studying the functions of the Aeromonas salmonicida A-layer and identifying A-layer structurefunction relationships (Garduño et al 1995).…”

mentioning

confidence: 99%

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

Lund¹,

Mikkelsen²,

Schrøder³

2009

Atypical furunculosis caused by atypical Aeromonas salmonicida bacteria is reported as an increasing problem in farmed Atlantic cod Gadus morhua in Norway. At present, furunculosis vaccines adapted for cod or other marine fish species are not available. To identify bacterial components important for inducing protection in cod, we compared oil-adjuvanted vaccines based on A. salmonicida isolates phenotypically differing in their major cell surface constituents, such as the Alayer protein and lipopolysaccharide O-chains. Also included was an A-layer-deficient isolate with physically reattached A-layer protein. Vaccines containing A. salmonicida A-layer-producing cells elicited significantly better protection than vaccines with A-layer-deficient cells or with a supernatant with secreted A-layer protein. The A. salmonicida cells with reattached A-layer-protein resulted in significant and equal protection to the A-layer-producing cells and protected significantly better than the A-layer-deficient isolate. These results indicate that the A-layer protein when attached to the cell surface plays a role in inducing protective immunity in cod. KEY WORDS: Atlantic cod · Aeromonas salmonicida · Furunculosis · Vaccine · A-layer protein Resale or republication not permitted without written consent of the publisherDis Aquat Org 85: [115][116][117][118][119][120][121][122] 2009 protection in salmonids. Furthermore, a correlation between survival rates and corresponding antibody levels to the A-layer protein has been found in Atlantic salmon Salmo salar and goldfish Carassius auratus (Midtlyng et al. 1996, Sinyakov et al. 2002. Earlier studies have shown that A-layer-possessing Aeromonas salmonicida used in oil-adjuvanted vaccines elicit acceptable protection against homologous challenge in salmon, as well as in marine fish species. However, vaccines based on A-layer-deficient isolates failed to protect in salmon and protected poorly or not at all in cod and Atlantic halibut Hippoglossus hippoglossus (Lund et al. 2003a,b, Mikkelsen et al. 2004, Lund et al. 2008a.Various A-layer functions have been identified by using A-layer-deficient mutants. In addition, physical reconstitution of the A-layer proved to be a useful tool in studying the functions of the Aeromonas salmonicida A-layer and identifying A-layer structurefunction relationships (Garduño et al. 1995). Mutations leading to lipopolysaccharide (LPS) O-chain-deficient strains gave rise to A-layer-deficient strains that released free sheets of assembled A-layer into the culture medium. This led to the assumption that LPS Ochains were involved in tethering the A. salmonicida A-layer to the bacterial outer membrane (Belland & Trust 1985, Dooley et al. 1989. A. salmonicida strains lacking the A-layer, but possessing the LPS O-chain, rapidly absorbed secreted A-protein at the cell surface to coat the cells with a single confluent layer (Griffiths & Lynch 1990). Physical reconstitution of the A-layer could be achieved by co-culturing A. salmonicida Alayer donor and re...