Abstract

Mycobacteriosis is an economically important bacterial disease of virtually all species of freshwater, brackish and marine fish (1). It is usually caused by Mycobacterium marinum, M. fortuitum, or M. chelonae and is a chronic progressive disease, leading to systemic infections and ultimately death. While the host's immune response against aquatic Mycobacterium spp. Has been characterized (2,3), an effective vaccine against mycobacteriosis has not been developed.

A vaccine for aquatic mycobacteriosis was created using a Mycobacterium spp. 85A antigen and Brucella abortus as the delivery vector. Previous studies in this laboratory have established that striped bass, Morone saxatilis, are particularly susceptible to Mycobacterium spp (4). Therefore, juvenile striped bass were used as a model to test the vaccine. Intraperitoneal vaccinations were administered on days 0, 14, and 35 with bacterial concentrations ranging from 10⁶ through 10¹⁰ long with a sham-inoculated saline control group. On days 0, 14, 35, and 49, blood was drawn from the caudal vessels of the fish for ELISA evaluation. Data from the ELISA exhibited a significant humoral antibody response to the 85A antigen and B. abortus antigen among the 10⁸, 10⁹, and 10¹⁰ groups.

On day 49, fish were challenged with an intramuscular injection of M. marinum at a concentration of 1.6 x 10⁶ colony-forming units per fish. Moribund fish were euthanized and routine histological examination performed to assess the protection conferred by the vaccine. In addition, on day 56, the anterior kidney was harvested from a sub-sample of each group of fish for a lymphoproliferative assay. This was used to assess the cell-mediate immune response elicited by the vaccine.

The long-term goal of this project is to create a safe, effective, marketable vaccine which will 1) decrease financial losses due to mycobacteriosis, 2) improve the overall health and immuno-competence of economically-important cultured marine food fish, 3) decrease antibiotic use in food fish, and 4) provide a protocol for developing fish vaccines against other significant intracellular pathogens.

References

1.  Austin, B. and D.A. Austin. 1993. Mycobacterium spp. In: Austin, B. and D.A. Austin (eds) Bacterial Fish Pathogens" Disease in Farmed and Wild Fish. Ellis Horwood, New York, N.Y.

2.  Bartos, J.M. and C.V. Sommer. 1981. In vivo cell mediated immune response to M. tuberculosis and M. salmoniphilum in rainbow trout (Salmo gairdneri). Developmental and Comparative Immunology 5:75-83.

3.  Chen, S.C., T. Yoshida, A. Adams, K.D. Thompson, and R.H. Richards. 1996. Immune response of rainbow trout to extracellular products of Mycobacterium spp. Journal of Aquatic Animal Health 8:216-222.

4.  Wolf, J.C. and S.A. Smith. 1999. Comparative severity of experimentally induced mycobacteriosis in striped bass Morone saxatilis and hybrid tilapia Oreochromis spp. Diseases of Aquatic Organisms 38: 191-200.