immune-enhancing and protective effects of lactobacillus delbrueckii bulgaricus on common carp vaccinated against aeromonas hydrophila

In this study, effect of lactobacillus delbrueckii bulgaricus (l. bulgaricus), both in its free form and microencapsulated with alginate/chitosan, on immunity and efficacy of  aeromonas hydrophila vaccine was assessed in common carp. a total of 360 common carp (48±5.1 g) were randomly divided in four groups, each in tree replicates. groups 1 to 3 were vaccinated against a. hydrophila and fed diets supplemented with basal diet, l. bulgaricus-treated feed, and encapsulated l. bulgaricus -treated feed, respectively, and group 4 was considered as the control. samples were taken on days zero, 30 and 60 of the experiment. growth performance indices (including fcr, sgr, per, and fer) and immunological parameters (antibody titer, serum lysozyme, complement and bactericidal activity, nbt reduction, globulin levels, and myeloperoxidase activity) were evaluated. additionally, hematological parameters (rbc, wbc, hb, and hct), intestinal enzyme activities (lipase, protease, amylase, and alp), antioxidant status (maladeyaldehide (mda) levels, superoxide dismutase (sod), glutathione (gsh), and catalase activity), and serum biochemical indices (glucose, urea, calcium, triglycerides, alp, cpk, and bilirubin) were compared among the groups. on day 60 of the experiment, the remaining fish in each group were challenged with virulent a. hydrophila, and cumulative mortality was recorded over a 14-day period. the results indicated that group 3 exhibited the highest growth indices and intestinal enzyme activity. most of the immune parameters showed a significant increase in groups 3 and 2 compared to control group (p<0.05). hematological and biochemical parameters remained consistent across all groups (p>0.05). following the challenge, the mortality rates were lower in groups 3 (20%) and 2 (30%) compared to control group (60%). overall, these data exhibited that administration of l. bulgaricus is able to enhance efficacy and immunogenicity of injectable a. hydrophila vaccine. also, alginate/chitosan-microencapsulation of this probiotic further amplifies its positive effects on the vaccine’s efficacy.