Subunit vaccine candidates against Aeromonas salmonicida in rainbow trout Oncorhynchus mykiss

PLoS One. 2017 Feb 9;12(2):e0171944. doi: 10.1371/journal.pone.0171944. eCollection 2017.

Abstract

Aeromonas salmonicida subsp. salmonicida is the etiological agent of furunculosis and a major fish health problem in salmonid aquaculture worldwide. Injection vaccination with commercial mineral oil-adjuvanted bacterin vaccines has been partly successful in preventing the disease but in Danish rainbow trout (Oncorhynchus mykiss, Walbaum) aquaculture furunculosis outbreaks still occur. In this study we tested the efficacy of experimental subunit vaccines against A. salmonicida infection in rainbow trout. We utilized in silico screening of the proteome of A. salmonicida subsp. salmonicida strain A449 and identified potential protective protein antigens that were tested by in vivo challenge trial. A total of 14 proteins were recombinantly expressed in Escherichia coli and prepared in 3 different subunit vaccine combinations to immunize 3 groups of rainbow trout by intraperitoneal (i.p.) injection. The fish were exposed to virulent A. salmonicida 7 weeks after immunization. To assess the efficacy of the subunit vaccines we evaluated the immune response in fish after immunization and challenge infection by measuring the antibody levels and monitoring the survival of fish in different groups. The survival of fish at 3 weeks after challenge infection showed that all 3 groups of fish immunized with 3 different protein combinations exhibited significantly lower mortalities (17-30%) compared to the control groups (48% and 56%). The ELISA results revealed significantly elevated antibody levels in fish against several protein antigens, which in some cases were positively correlated to the survival.

MeSH terms

  • Aeromonas salmonicida / immunology*
  • Aeromonas salmonicida / pathogenicity
  • Animals
  • Antibodies, Bacterial / immunology
  • Bacterial Proteins / immunology
  • Fish Diseases / immunology*
  • Fish Diseases / prevention & control
  • Gram-Negative Bacterial Infections / immunology*
  • Gram-Negative Bacterial Infections / prevention & control
  • Immunization / methods
  • Oncorhynchus mykiss / immunology*
  • Oncorhynchus mykiss / microbiology
  • Proteome / immunology
  • Vaccines, Subunit / immunology*

Substances

  • Antibodies, Bacterial
  • Bacterial Proteins
  • Proteome
  • Vaccines, Subunit

Grants and funding

This study was funded by from the Danish Council for Strategic Research under the PROFISH project (Grant No. DSF: 11-116252) and the European Commission FP7 project Targetfish (Grant No. 311993). The funder provided support in the form of salaries for authors [MHM], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. The commercial affiliation (Evaxion Biotech) did not provide financial support in this study. The commercial affiliation (Evaxion Biotech) provided the protein sequences tested in this study but played no role in data collection, analysis or decision to publish.