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United States Department of Agriculture

Agricultural Research Service

Research Project: VACCINOLOGY AND IMMUNITY OF AQUATIC ANIMALS Title: Immunogenic and Protective Effects of a DNA Vaccine for Mycobacterium Marinum in Fish

Authors
item Pasnik, David
item Smith, Stephen - VMRCVM, VPI&SU

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2004
Publication Date: February 10, 2005
Citation: Pasnik, D.J., Smith, S.A. 2005. Immunogenic and protective effects of a dna vaccine for mycobacterium marinum in fish. Veterinary Immunology and Immunopathology. 103 (2005) 195-206.

Interpretive Summary: Piscine mycobacteriosis is a common bacterial disease of fishes caused by Gram-positive, acid-fast Mycobacterium spp., commonly Mycobacterium marinum. These bacteria can cause a chronic progressive, often fatal disease, causing granulomatous inflammation in virtually any tissue. Given its ubiquitous nature in water and sediment, this group of organisms has been reported worldwide in over 160 species of fresh and saltwater fish. Presently, no chemotherapeutic agents are approved for treatment of mycobacteriosis in foodfish in the United States. Because of the difficult management of aquatic mycobacteriosis and due to its human zoonotic potential, development of an effective vaccine against fish mycobacteria is vital. There are numerous commercially available bacterins for bacterial fish pathogens, yet none exists for aquatic mycobacteriosis. A DNA vaccine was constructed using the Mycobacterium marinum Ag85A gene that encodes one of the major secreted fibronectin-binding proteins of Mycobacterium spp., which was isolated and then subcloned into a commercially available eukaryotic expression vector. Juvenile hybrid striped bass (Morone saxatilis x M. chrysops), a species known to be particularly susceptible to this disease, were immunized by injection with the resulting construct and as a result produced specific immune responses towards the Ag85A. Increasing concentrations of antibodies were generated in all DNA vaccine groups, while macrophage phagocytosis and respiratory burst functions failed to exhibit upregulation after vaccination. In addition, fish receiving the DNA vaccine developed a protective response to a live M. marinum challenge 90 days post-inoculation, as demonstrated by increased survival of vaccinated fish over control fish and by reduced splenic bacterial counts in vaccinated fish.

Technical Abstract: Mycobacteriosis, caused by numerous Mycobacterium spp., can be a devastating disease of both wild and cultured fishes. As no efficacious treatment exists, a vaccine against fish mycobacteriosis is essential for prevention and control of this disease. Thus, a DNA vaccine was constructed using the Mycobacterium marinum Ag85A gene that encodes one of the major secreted fibronectin-binding proteins of Mycobacterium spp., which was isolated and then subcloned into a commercially available eukaryotic expression vector. Juvenile hybrid striped bass (Morone saxatilis x M. chrysops), a species known to be particularly susceptible to this disease, were immunized by i.m. and i.p. injection with the resulting construct and as a result produced specific immune responses towards the Ag85A. Increasing concentrations of humoral antibodies to the Ag85A antigen were generated in all DNA vaccine groups, while macrophage phagocytosis and respiratory burst functions failed to exhibit upregulation after vaccination. In addition, fish receiving the DNA vaccine developed a protective response to a live M. marinum challenge 90 days post-inoculation, as demonstrated by increased survival of vaccinated fish over control fish and by reduced splenic bacterial counts in vaccinated fish. Furthermore, humoral immune responses and protective effects were significantly increased at higher vaccine doses using the i.m. injection route

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