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The molecular characteristics of Yersinia ruckeri such as total proteins (TP), outer membrane proteins OMP) and lipopolysaccharides (LPS) in 34 isolates from rainbow trout farms in Tehran, Mazandaran and Zanjan provinces were determined, using SDS-PAGE method. The molecular weight (MW) for TP of all bacterial isolates was mostly less than 100 KD with a banding density in range 28 to 100 KD. Also, protein pattern of OMP consisted of three major bands with MW of 28-35 KD (two bands) and 10-17 KD (one band) plus some minor bands with MW of 48-75 KD and 17-28 KD. In addition, the LPS pattern of all bacterial isolates were less than 130 KD with the most band density in range 28-100 KD. These results show that the banding profile of TP, OMP and LPS of all isolates of Y. ruckeri were identical, demonstrating minimum heterogeneity among Iranian isolates of Y. ruckeri. Therefore, it is feasible for the formulation of a monovalent vaccine to yersiniosis in future.

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The present study intends to assess the effects of Na diformate oral use with citric acid on some skin mucosal immunity indices (total protein, total immunoglobulin (TIg), lysozyme, protease, esterase, and alkaline phosphatase (ALP)) of rainbow trout following experimental challenge with Yersiniosis agent (Yersinia ruckeri). Subsequent to the determination of the 7-day median lethal dose (LD50) of Yersinia ruckeri, fish were stocked in eight groups and two repetitions. The acidifiers separately with a dose of 0.2%, and combined 0.1+0.1% was added to the commercial diet. Five days after inoculation, feeding of fish with acidifiers commenced, and following 15 days, the mucus samples were gathered from the skin of anesthetized fish to measure immune indices. Results showed that the 7-day LD50 of Y. ruckeri was 8.91×105 CFU/ml. In the main experiment, findings indicated the significant effect of Na diformate on the increased levels of mucoid total protein and proteolytic activity of healthy or diseased fish. The acidifiers-contained diet because of potentially having synergistic effect caused inducing the mucus TIg. It seems that the orally use of Na difirmate in 0.2% of the diet separately or combined with citric acid, at least for 15 days, can improve the cutaneous mucus immunological indices that its result is an increase in the survival rate of farmed rainbow trout.