Effect of the Human Probiotic Bacterium Escherichia coli Nissle (1917) on performance and immune response of Nile tilapia Oreochromis niloticus

If a human probiotic is beneficial for fish, its incorporation into diets would be much easier to accept. The present work assessed the effect of human probiotic Escherichia coli Nissle 1917 (EcN) on growth, feed conversion and immune response of Nile tilapia Oreochromis niloticus. Diets with various EcN concentrations were offered to fish for 8 weeks. The fish were also challenged with pathogenic bacteria to assess whether EcN improved immunity. Dietary EcN did not affect survival and growth. Hematology suggests an effect on the immune system but EcN did not improve survival of challenged tilapia. Accordingly, the immune response was probably targeting the EcN itself. A decrease in respiratory burst was probably caused by the iron chelating systems of EcN, while decrease in liver weight was related to intestinal inflammation and stress caused by the EcN. Tilapia appear not to harbor intestinal Escherichia coli even when surrounding water is replete.