Pathogenic Streptococcus in Tilapia: Rapid Diagnosis, Epidemiology and Pathophysiology
Budget
Duration
$230,000
3
years
Bercovier, H.
Hebrew U
Frelier, F.P.
Texas A&M
Final Report Abstract Within the project "Pathogenic Streptococcus in Tilapia", gram positive cocci pathogens of fish in Israel and in the United States were characterized. We showed that Streptococcus shiloi, the name for an agent causing septicemic infection in fish, is a junior synonym of Streptococcus iniae and that Enterococcus seriolicida is a junior synonym of Lactococcus garvieae, a causative agent of septicemia and meningo-encephalitis in fish. Molecular epidemiology studies on these two pathogens, based on 16S rDNA sequences and ribotyping showed that although each country had specific clones, S. iniae originated probably from the U.S. and L. garvieae from Japan. PCR assays were developed for both pathogens and applied to clinical samples. S. agalactiael S. difficile was also recognized for the first time in the U.S. in tilapia. Our histopathological studies explained the noted paradox (abundant in vitro growth often accompanied by scant to small numbers of organisms within the meninges in histologic sections of brain) in diagnostic of fish streptococcus. The greatest concentration of cocci were consistently observed within macrophages infiltrating the extrameningeal fibroadipose tissue surrounding the brain within the calvarium. These results also suggests that the primary route of meningeal infection may be extension from the extrameningeal connective tissue rather than meningeal vascular emigration of cocci-containing macrophages.
Our work has resulted in a cognizance of streptococcus as fish pathogen which goes beyond the pathology observed in tilapia and is already extended to many aquaculture fish species in Israel and in the United States. Finally, our data suggest that vaccines (bivalent or trivalent) could be developed to prevent most of the damages caused by streptococcus in aquaculture.