An Experimental Study of the Effects of Lactobacillus Acidophilus and Lactobacillus Plantarum Probiotic Bacteria on the Immune System, Growth Factors, and Disease Resistance in the Rainbow Trout

The present study aimed to examine the effects of Lactobacillus acidophilus and Lactobacillus plantarum probiotics separately and synergistically on the immune system, growth factors, and disease resistance in the rainbow trout.

At in vitro level, bacteriocin extracts of the target bacteria were used in the antimicrobial test against the fish pathogen Aeromonas hydrophila. Next, their effects on the fish blood lymphocytes were evaluated. At in vivo level, after feeding the fish in each treatment with the lactobacilli at the concentration of 108 CFU g-1 for 60 days, the growth indices were calculated. Then, blood samples from the rainbow trout were used to analyze any increase in the number of lymphocytes. Furthermore, given the infectious challenge with the pathogen Chryseobacterium aquaticum, the survival rates of the fish were determined.

L. acidophilus had the best effect on the growth factors and significantly increased the number of fish blood lymphocytes (p <0.05). The broth microdilution assay also was shown to reduce the amount of A. hydrophila colonies by more than 90%. Treatment with this lactobacillus species produced the highest survival rate with this infectious challenge. Then, the synergistic and the L. plantarum treatments were analyzed, respectively, which each showed a significant increase in the indices under study.

According to obtained results, it might be concluded that the feeding by L. acidophilus could likely enhance the immune responses and growth indices in fish both separately and synergistically with L. plantarum.