薰衣草精油对嗜水气单胞菌的抑制作用及对斑马鱼模型免疫力的影响OACHSSCD

[Objective]This study aims to evaluate the antibacterial activity of lavender(Lavandula angustifolia Mill.)essential oil against a highly virulent bacterium,Aeromonas hydrophila,isolated from the intestine of red claw crayfish(Cherax quadricarinatus),and to assess safety and immunoprotective effects of the essential oil in a zebrafish(Danio rerio)infection model,thereby providing a theoretical basis for developing natural and eco-friendly disease control strategies in aquaculture.[Methods]Strain 171215-1 was isolated on thiosulfate-citrate-bile salts-sucrose(TCBS)agar medium,and identified based on morphological features,physiological and biochemical characteristics,and 16S rDNA phylogenetic analysis.The antibacterial activity of lavender essential oil was determined using the Oxford cup method,disk diffusion assay,and broth microdilution to obtain the minimum inhibitory concentration(MIC),and the expression changes of virulence genes were analyzed by quantitative real-time PCR(RT-qPCR).Using zebrafish as a model,the effects of different doses of lavender essential oil on post-challenge survival,antioxidant indices,and the expression of antioxidant-and immune-related genes,including sod,cat,and gsh-px,were evaluated.[Results]Based on morphological,physiological and biochemical characteristics,and 16S rDNA phylogenetic analysis,strain 171215-1 was identified as Aeromonas hydrophila and exhibited resistance to multiple classes of antibiotics.In the pathogenicity test,intraperitoneal injection with 1.5×10⁶ CFU/mL A.hydrophila 171215-1 resulted in a cumulative mortality of(38.33±1.44)％,whereas the 0.5×10⁷ and 1.5×10⁷ CFU/mL groups reached 100％mortality within 2 days.Lavender essential oil exhibited dose-dependent antibacterial activity against this strain,with a MIC of 0.5 mg/mL;in the Oxford cup assay,the diameter of the inhibition zone increased significantly from(14.42±0.82)mm to(40.12±0.58)mm as the sample volume increased from 20 μL to 100 μL.At sub-inhibitory concentrations 0.002 5％、0.005 0％ and 0.010 0％,the relative expression levels of the virulence-related genes hlyA,aerA,ahyB,and ompA were significantly reduced by approximately 30％-65％(P<0.05).In the safety test,dietary supplementation with lavender essential oil resulted in overall low mortality across treatments,with a mortality rate of 0.83％at dietary inclusion levels of≤0.010％.In the infection model,fish fed with a diet containing lavender essential oil at a mass fraction of 0.005％achieved a survival rate of 100.0％,which was significantly higher than that of the positive control(68.89±0.96)％(P<0.05).Moreover,compared with the positive control,this treatment increased hepatic antioxidant enzyme activities and total antioxidant capacity by approximately 20％ to 150％,reduced malondialdehyde levels by approximately 30％ to 45％,and significantly downregulated the expression of inflammation-related genes by approximately 3％ to 50％(P<0.05).[Conclusion]Lavender essential oil can inhibit multidrug-resistant A.hydrophila in vitro and suppress the expression of key virulence genes.In vivo,it enhanced antioxidant defenses and alleviated inflammatory responses,thereby improving zebrafish resistance to infection.An integrated assessment indicated that the optimal dietary inclusion level of the essential oil is 0.005％.