Non-infectivity of cattle Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus and channel catfish, Ictalurus punctatus

Streptococcus agalactiae is classified as a Lancefield's group B Streptococcus. It is one causative bacterium of streptococcosis that is responsible for severe economic losses in wild and cultured fish worldwide. S. agalactiae also causes bovine mastitis. No information is available on infectivity of cattle S. agalactiae isolates in fish. In the present study, the results showed that 10 cattle isolates from 8 different dairy farms were not infectious in Nile tilapia (Oreochromis niloticus) or channel catfish (Ictalurus punctatus) at greater than 108 colony forming units per fish. S. agalactiae was not re-isolated from the brain or head kidney of the fish at 24 and 48 h post-injection.