Submitted to: Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/25/2008
Publication Date: 6/19/2008
Citation: Garcia, J.C., Klesius, P.H., Evans, J.J., Shoemaker, C.A. 2008. Non-infectivity of cattle Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus and channel catfish, Ictalurus punctatus. Aquaculture. 281:151-154. Interpretive Summary: Streptococcus agalactiae is highly infectious in many species of cultured and wild fish. The U.S. and worldwide aquaculture industries are severely affected and economic losses are the hundred of million dollars, annually. It is also a causative agent of bovine mastitis and may be isolated from the milk of an infected cow. Only limited comparative information is available on the phenotypic characteristics between fish and cattle isolates of S. agalactiae and no information is available is available on infectivity of cattle isolates in fish. The phenotypic characteristics of fish and cattle isolates were found to be different and could be distinguished from each other by capsular serotype, CAMP factor, D-lactose and D-Trehalose fermentation and growth pattern in fluid medium. The cattle isolates were found not to be infectious for Nile tilapia and channel catfish. It is unlike that cattle with mastitis are a source of S. agalactiae in cultured fish.
Technical Abstract: Streptococcus agalactiae is classified as a Lancefield’s group B Streptococcus (GBS). It is the causative bacterium of streptococcosis that is responsible for severe economic losses in wild and cultured fish, worldwide. Streptococcus agalactiae also causes bovine mastitis. Only limited comparative information is available on the characteristics of fish and cattle GBS isolates and no information is available on infectivity of cattle GBS isolates in fish. In the present study, GBS isolates from fish (n=36) and cattle GBS isolates (n=10) were found to have a number of common phenotypic characteristics of the S. agalactiae reference strains (n=4). However, the phenotypic characteristics of these GBS isolates were different from the reference strains of Streptococcus agalactiae (n=5), S. dysagalactiae (n=2), Streptococcus phocae (n=1) and Lactococcus garvieae (n=1). The results showed that GBS isolates of fish and cattle origins could be distinguished from each other by capsular serotype, CAMP factor, D-lactose and D-trehalose fermentation and growth pattern in fluid medium. Ten cattle isolates were not found to be infectious in Nile tilapia (Oreochromis niloticus) and channel catfish (Ictalurus punctatus). Cattle GBS isolates were not cultured from the brain or head kidney of the fish at 24 and 48 hour post-injection.