Effects of Lipopolysaccharides (LPS) of Yersinia ruckeri on Immune Response in Rainbow Trout (Oncorhynchus mykiss) by Intraperitoneal and Oral Administration

BACKGROUND: Yersinia ruckeri (Y. ruckeri) is an important fish pathogen, which has received more attention recently due to the increasing economic losses in the rainbow trout industry worldwide. Nowadays researching on novel oral vaccines is expanding due to convenience and ease of administration. OBJECTIVES: In the present study, the effect of Y. ruckeri lipopolysaccharide (LPS) on Protective immunity of the Y. ruckeri bacterin was evaluated in rainbow trout. METHODS: For this purpose, 720 juvenile rainbow trout were randomly divided into 8 groups each in triplicates. Group G1 to G4 received respectively PBS, bacterin, LPS and Bacterin+ LPS by intraperitoneal route. Groups 5 to 8 received respectively PBS, bacterin, LPS and Bacterin+ LPS by meal. On day 60 after immunization, half of the fish in each treatment was challenged intraperitoneally and the remaining half of fish in the oral receiving bacterin groups were challenged by bath method with 1 LD50 and 1 LC50 of a Y. ruckeri local virulent isolate respectively. RESULTS: The ELISA results indicated that LPS via oral route did not increase the humoral immune response in serum, but LPS with the FKC could increase antibody levels significantly in serum and mucus (P<0.05). According to the results after I.P. challenge, in G2 to G4 groups survival rate was 76.47, 58.82 and 52.94 percent respectively, which was significantly higher (P<0.05) than G5 to G7 groups with 25, 17.65, 35.29 percent survival rate. The survival rate after bath challenge was 37.5, 49.49 and 29.49 in groups G5 to G7, respectively, which was significantly (P<0.05) more than the control group (G1). CONCLUSIONS: The results showed that LPS has a significant effect on the induction of protective immunity to Y. ruckeri bacterin principally via I.P. route. Because of acceptable protection, the above method can be a promising and novel candidate to control yersiniosis in rainbow trout.