ABSTRACT: This study investigated the antifungal activity of 5 essential oils (EOs) towards yeasts recovered from diseased fishes; and focused on the efficacy of one EO (carvacrol) on growth performance, non-specific immunity, and disease resistance of Nile tilapia Oreochromis niloticus against Cryptococcus uniguttulatus challenge. Thymoquinone, thymol, carvacrol, eugenol, and cinnamon were first tested in vitro against 20 clinical yeast strains in comparison with antifungal drugs (fluconazole, ketoconazole, itraconazole, amphotericin B, nystatin, and clotrimazole) using disc diffusion and broth microdilution methods. For the in vivo challenge, fish (n = 150) were divided into 5 groups (carvacrol prophylaxis, carvacrol treatment, itraconazole treatment, unchallenged control, and positive control; 30 fish group^-1) with 3 replicates. Phagocytic activity, reactive oxygen species production, reactive nitrogen species production, myeloperoxidase, lysozyme activity, and total immunoglobulins were tested before and after challenge. Relative percent survival (RPS) and mortality percent were determined as indicators for functional immunity. EOs displayed divergent degrees of antifungal activity, and carvacrol was the most effective against the tested yeasts. The dietary additive of carvacrol significantly enhanced growth performance, all immunological parameters, and the RPS values (90%) compared to other treatments. This unique experimental model indicates that carvacrol seems promising not only for enhancing immunity and promoting fish growth, but also for controlling emerging fungal infections. Future studies should investigate different concentrations of carvacrol as well as its antifungal activity in different fish species.

中文翻译：

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香芹酚精油刺激尼罗罗非鱼对隐球菌感染的生长性能，免疫反应和耐受性。

摘要：这项研究调查了5种精油（EOs）对从患病鱼类中回收的酵母的抗真菌活性。并集中于一种EO（香芹酚）对尼罗罗非鱼Oreochromis niloticus对抗隐球菌挑战的生长性能，非特异性免疫和抗病性的功效。首先采用圆盘扩散和肉汤微稀释方法，与抗真菌药（氟康唑，酮康唑，伊曲康唑，两性霉素B，制霉菌素和克霉唑）相比，对20种临床酵母菌株进行了体外测试的百里醌，百里酚，香芹酚，丁香酚和肉桂粉。对于体内挑战，将鱼（n = 150）分为5组（香芹酚预防，香芹酚治疗，伊曲康唑治疗，无挑战性对照和阳性对照）； 30条鱼^-1组），重复3次。在攻击之前和之后测试吞噬细胞活性，活性氧产生，活性氮产生，髓过氧化物酶，溶菌酶活性和总免疫球蛋白。确定相对存活率（RPS）和死亡率百分比作为功能性免疫的指标。EOs显示出不同程度的抗真菌活性，香芹酚对测试的酵母最有效。与其他疗法相比，香芹酚的膳食添加剂显着提高了生长性能，所有免疫学参数和RPS值（90％）。这个独特的实验模型表明香芹酚不仅有望增强免疫力和促进鱼类生长，而且还有望控制新兴的真菌感染。