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Title: Immunization with recombinant aerolysin and hemolysin protected channel catfish against virulent Aeromonas hydrophila

Author
item Zhang, Dunhua
item Xu, Dehai
item Shoemaker, Craig

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2015
Publication Date: 11/12/2015
Citation: Zhang, D., Xu, D., Shoemaker, C.A. 2015. Immunization with recombinant aerolysin and hemolysin protected channel catfish against virulent Aeromonas hydrophila. Aquaculture Research. doi: 10.111/are.12931.

Interpretive Summary: Aeromonas hydrophila is a ubiquitous gram-negative bacterium of aquatic environments. The bacterium has long been implicated as a causative agent of fish disease named as motile aeromonad septicemia (MAS). MAS was not a major concern until 2009, when MAS outbreaks occurred, resulting in losses of food-sized catfish totaling over 8 million pounds in the Southeastern United States. Studies found that isolates from diseased catfish of recent epidemic outbreaks are a clonal group of highly virulent A. hydrophila. There is currently no effective prevention method to control this disease. In this study, two protein toxins, commonly found in virulent A. hydrophila, was produced in large quantity using Escherichia coli expression system. Experimental fish were immunized with these E. coli expressed recombinant aerolysin and hemolysin (rArl and rHly). Two weeks after immunization, the fish were challenged with virulent A. hydrophila. Results showed that fish immunized had significantly higher survival rate following challenge, compared with sham-immunized fish. Therefore, both rArl and rHly are proved to be potential immunogens that can be used for development of recombinant protein vaccines.

Technical Abstract: Aeromonas hydrophila is emerging as one of the major concerns in catfish aquaculture in the Southeastern United States due to recent outbreaks of motile aeromonad septicemia (MAS) caused by virulent clonal isolates. There is no effective vaccine currently available for the prevention of MAS. In this study, two virulence-associated proteins of A. hydrophila, aerolysin and hemolysin, were heterologously expressed in Escherichia coli cells. Recombinant aerolysin (rArl) and hemolysin (rHly) were used to immunize catfish. Both rArl and rHly induced humoral immune response as evidenced by immunoblotting and cell agglutination; immunized fish had significantly less mortality as compared to control fish upon challenge with virulent A. hydrophila. When mixture of rArl and rHly was used to immunize the fish, significantly higher relative percent survival (RPS) was obtained. Sustained RPS of 71-78% were observed at 2-5 weeks post immunization. The results of this study indicated that immunization against aerolysin and hemolysin had significant impact on the establishment of pathogenesis by A. hydrophila, suggesting that these two proteins could serve as general immunogens for future development of recombinant protein vaccines.