Increasing of temperature induces pathogenicity of Streptococcus agalactiae and the up-regulation of inflammatory related genes in infected Nile tilapia (Oreochromis niloticus)

Temperature strongly affects the health of aquatic poikilotherms. In Nile tilapia (Oreochromis niloticus), elevated water temperatures increase the severity of streptococcosis. Here we investigated the effects of temperature on the vulnerability and inflammatory response of Nile tilapia to Streptococcus agalactiae (Group B streptococci; GBS). At 35 and 28 degrees C, CBS took 4 and 7 h, respectively to reach the log-phase and, when incubated with tilapia whole blood, experienced survival rates of 97% and 2%, respectively. The hemolysis activity of GBS grown at 35 degrees C was five times higher than that of GBS grown at 28 degrees C. GBS expressed cylE (beta-hemolysinicytolysin), cfb (CAMP factor) and PI-2b (pilibackbone) much more strongly at 35 degrees C than at 28 degrees C. Challenging Nile tilapia reared at 35 and 28 degrees C with GBS resulted in accumulated mortalities of about 85% and 45%, respectively. At 35 degrees C, infected tilapia exhibited tremendous inflammatory responses due to a dramatic up-regulation (30-40-fold) of inflammatory-related genes (cyclooxygenase-2, IL-1 beta and TNF-alpha) between 6 and 96 h-post infection. These results suggest that the increase of CBS pathogenicity to Nile tilapia induced by elevated temperature is associated with massive inflammatory responses, which may lead to acute mortality. (C) 2014 Elsevier B.V. All rights reserved.