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In recent years, probiotics, especially lactic acid bacteria, have been used as dietary supplements to protect fish from various infections. Here, we examined the protective effects of Lactobacillus rhamnosus against experimental Edwardsiella tarda infection in tilapia (Oreochromis niloticus). Cumulative mortality was significantly lower in probiotic-supplemented fish than in control fish. In a histopathological survey, pyogranulomatous responses were observed at an earlier stage and to a greater extent in the probiotic-supplemented fish than in the control fish. Immunohistochemistry using an anti-E. tarda antibody revealed a larger number of positive signals in pyogranuloma-participating cells, indicating an enhanced phagocytic ability. Alternative complement activity was significantly higher in the probiotic groups than in the control. These results suggest that L. rhamnosus enhanced the alternative complement system of the fish, enabling phagocytic cell aggregation, increasing phagocytic activity and subsequently protecting the fish from acute septicemic death by E. tarda infection. Prevention of thymic necrosis by the probiotic supplement seems to minimize immunosuppression and to initiate an immune response against edwardsiellosis.

Research Insights

SupplementHealth OutcomeEffect TypeEffect Size
Lactobacillus rhamnosusImproved Phagocytic ActivityBeneficial
Lactobacillus rhamnosusIncreased Alternative Complement ActivityBeneficial
Lactobacillus rhamnosusReduced Colitis-Related MortalityBeneficial
Lactobacillus rhamnosusReduced Thymic NecrosisBeneficial
Lactobacillus rhamnosus DSM33560Improved Phagocytic FunctionBeneficial
Lactobacillus rhamnosus DSM33560Increased Alternative Complement ActivityBeneficial
Lactobacillus rhamnosus DSM33560Reduced Colitis-Related MortalityBeneficial
Lactobacillus rhamnosus DSM33560Reduced Thymic NecrosisBeneficial
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