| Summary: | The objective of the study was to evaluate the nanoemulsion of the essential oil of Cymbopogon flexuosus (EOCF) as an aquaculture feed additive, through several biological models. The antioxidant capacity, its impact on zootechnical performance, and the changes it generates in the gastrointestinal tract were evaluated in silver catfish (Rhamdia quelen) naturally infected with Aeromonas. The antimicrobial activity of EOCF nanoemulsions was evaluated in pathogenic bacteria affecting fish (Aeromonas salmonicida, Aeromonas hydrophila, and Vibrio anguillarum). The cytotoxicity of the compound was evaluated in Atlantic Salmon Kidney (ASK) linear cells. The immunostimulatory capacity (response to bacterial adhesion and invasion) and cell viability were evaluated in primary Salmon salar macrophages and in ASK linear cells pretreated with the EOCF nanoemulsion and challenged with an infection of A. salmonicida. Supplementation with EOCF nanoemulsion in infected animals did not alter performance indicators (weight, lenght, etc.), reduced oxidative stress markers in muscle, maintained them in the liver, and treatment with 0.25 mL of EOCF nanoemulsion per kg diet stimulated the enzymatic activity of the antioxidant defense system such as superoxide dismutase, glutathione S-transferase and total antioxidant activity in muscle. As for gastrointestinal morphology, treatment with 0.5 and 1.0 mL of EOCF nanoemulsion per kg diet reduced the mean number of goblet cells and the height of the villi. In vitro models reported a minimum inhibitory concentration and minimum bacterial concentration of 390 µg mL-1 for A. salmonicida and A. hydrophila, and 190 µg mL-1 for V. anguillarum. In the cell lines, an IC50 of 120 µg mL-1 was reported and it was shown that at a concentration of 6 µg mL-1 the nanoemulsion of EOCF does not affect the cell viability of ASK cell lines and primary macrophages of S. salar. The latter cells showed that they increase bacterial adhesion when pretreated with this concentration but reduce the invasion of the ...
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