Subunit vaccine candidates against Aeromonas salmonicida in rainbow trout Oncorhynchus mykiss.

Moonika Haahr Marana,Louise Von Gersdorff Jørgensen,Jiwan Kumar Chettri,Kurt Buchmann,Per Walter Kania,Inger Dalsgaard,Andreas Holm Mattsson,Jakob Skov,Giuseppe Scapigliati

doi:10.1371/journal.pone.0171944

Moonika Haahr Marana, Louise Von Gersdorff Jørgensen + Show 7 more

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https://doi.org/10.1371/journal.pone.0171944

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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.

Highlights

Aeromonas salmonicida subsp. salmonicida is the causative agent of typical furunculosis in aquacultured salmonid fish
This study utilized recombinant proteins encoded by the genome of A. salmonicida subsp. salmonicida A449 for immunization against furunculosis
The in silico approach known as reverse vaccinology [54] has been used to identify vaccine candidates for bacterial fish diseases in few studies previously [55,56,57] but to the best of our knowledge—this is the first time it has been applied for A. salmonicida subsp. salmonicida

Summary

Introduction

Aeromonas salmonicida subsp. salmonicida (hereafter AS) is the causative agent of typical furunculosis in aquacultured salmonid fish. Salmonicida (hereafter AS) is the causative agent of typical furunculosis in aquacultured salmonid fish. Furunculosis causes bacterial septicemia that leads to significant economic losses due to fish morbidity and mortality [1]. Vaccination of salmonids against furunculosis is generally applied with injection vaccines containing formalin-killed AS bacteria combined with mineral oil adjuvant. Subunit vaccines against furunculosis in rainbow trout 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

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