Construction of Aeromonas salmonicida subsp. achromogenes AsaP1‐toxoid strains and study of their ability to induce immunity in Arctic char, Salvelinus alpinus L

• Published in: Journal of fish diseases 2015-10, Vol.38 (10), p.891-900
• Main Authors: Schwenteit, J M, Weber, B, Milton, D L, Bornscheuer, U T, Gudmundsdottir, B K
• Format: Article
• Language: English
• Subjects: achromogenes; Aeromonas salmonicida subsp; Aeromonas salmonicida subsp. achromogenes; Arctic char; AsaP1-toxoid; bacterin; extracellular otease AsaP1; extracellular protease AsaP1; fish production; furunculosis; immunity; lethal dose 50; mutants; Salvelinus alpinus; Salvelinus alpinus L; vaccines; virulence
• ISSN: 0140-7775; 1365-2761; 1365-2761
• DOI: 10.1111/jfd.12303

The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonicida subsp. achromogenes, expressed as a 37‐kDa pre‐pro‐peptide and processed to a 19‐kDa active peptide. The aim of this study was to construct mutant strains secreting an AsaP1‐toxoid instead of AsaP1‐wt, to study virulence of these strains and to test the potency of the AsaP1‐toxoid bacterin and the recombinant AsaP1‐toxoids to induce protective immunity in Arctic char. Two A. salmonicida mutants were constructed that secrete either AsaP1E₂₉₄A or AsaP1Y₃₀₉F. The secreted AsaP1Y₃₀₉F‐toxoid had weak caseinolytic activity and was processed to the 19‐kDa peptide, whereas the AsaP1E₂₉₄A‐toxoid was found as a 37‐kDa pre‐pro‐peptide suggesting that AsaP1 is auto‐catalytically processed. The LD₅₀ of the AsaP1Y₃₀₉F‐toxoid mutant in Arctic char was significantly higher than that of the corresponding wt strain, and LD₅₀ of the AsaP1E₂₉₄A‐toxoid mutant was comparable with that of an AsaP1‐deficient strain. Bacterin based on AsaP1Y₃₀₉F‐toxoid mutant provided significant protection, comparable with that induced by a commercial polyvalent furunculosis vaccine. Detoxification of AsaP1 is very hard, expensive and time consuming. Therefore, an AsaP1‐toxoid‐secreting mutant is more suitable than the respective wt strain for production of fish bacterins aimed to protect against atypical furunculosis.