Lactobacillus plantarum enhances immunity of Nile tilapia Oreochromis niloticus challenged with Edwardsiella tarda

Edwardsiella tarda is a bacterial fish pathogen associated with high mortality in aquaculture. Lactobacillus plantarum, which is a probiotic with immunomodulatory properties, was used to improve the disease resistant in Nile tilapia (Oreochromis niloticus). One hundred twenty O. niloticus (60 ± 5 g live body weight) were divided into four groups; the first (control) was fed on an unsupplemented diet, the second and the third group were fed on a diet supplemented with L. plantarum (1012 bacterial cells/kg feed) for two weeks (G1) and four weeks (G2), and the fourth group (G3) was fed on a diet supplemented with antibiotic florfenicol for ten days. Haemogram, liver enzymes (AST, ALT and ALP levels), hepatic antioxidant enzymes (GPx and CAT) and serum creatinine were measured to assess the impacts of the additives on the health status of fish. The level of gene expressions of interleukin beta 1 (IL-1β), tumour necrosis factor (TNF)-α and IL-10 was measured after supplementation and challenge tests. Fish were challenged with the obtained median lethal dose (LD50) of E. tarda (2.54 × 106 CFU/ml). O. niloticus fed on supplemented diets with L. plantarum G1 and G2 showed significantly enhanced immune status even after fourteen days of the experimental infection with E. tarda; however, florfenicol treatment G3 (mortality 20%) had exhibited lower MR% compared with L. plantarum groups (mortality 43.3% for both) and the control (mortality 60%). L. plantarum could protect O. niloticus against E. tarda infection compared to the control with a significant enhancement of fish health that helps in the restoration of normal physiological status.