Atypical Aeromonas salmonicida (aAs) is currently one of the most routinely recovered bacterial pathogens isolated during disease outbreaks in farmed cleaner fish, ballan wrasse (Labrus bergylta, Ascanius). Vibrionaceae family bacteria have also been isolated from ballan wrasse in Scotland. This study determined the infectivity, pathogenicity and virulence of aAs and Vibrionaceae isolates in juvenile farmed ballan wrasse (n = 50; approx. 2 g) using a bath challenge, and fish were monitored for a period of 16 days. Atypical As caused significant mortalities in contrast to Vibrionaceae isolates. Notably, differential virulence was observed between two aAs vapA type V strains at similar challenge doses. Diseased fish exhibited a systemic infection where aAs was detected in all analysed tissues (liver, spleen and kidney) by PCR and qPCR. Macroscopically, moribund and survivor fish exhibited hepatomegaly and splenomegaly. In moribund and surviving fish, histopathology showed granulomatous hepatitis with eosinophilic granular cells surrounding bacterial colonies and endocarditis along with splenic histiocytosis. This is the first report of a successful aAs bath challenge model for juvenile ballan wrasse which provides an important tool for future studies on vaccine efficacy and immunocompetence.

中文翻译：

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新型非典型气单胞菌鲑鱼浴挑战模型，用于少年巴兰濑鱼（Labrus bergylta，Ascanius）

非典型鲑鱼气单胞菌（a As）是目前养殖的清洁鱼Ballan濑鱼（Labrus bergylta，Ascanius）在疾病暴发期间分离出的最常规回收的细菌病原体之一。弧菌科细菌也已从苏格兰的巴兰濑鱼中分离出来。这项研究确定了砷和弧菌科分离株在幼稚养殖的巴兰濑鱼（n  = 50；约2 g）中的感染力，致病性和毒力，并进行了沐浴攻击，并对其进行了16天的监测。与弧菌科分离株相比，非典型As导致大量死亡。值得注意的是，在两个a As vapA之间观察到了不同的毒力相似激发剂量的V型毒株。患病鱼表现出全身感染，其中通过PCR和qPCR在所有分析的组织（肝脏，脾脏和肾脏）中检测到As。宏观上，垂死的和幸存的鱼表现出肝肿大和脾肿大。在垂死的和存活的鱼类中，组织病理学显示肉芽肿性肝炎，嗜酸性粒细胞围绕细菌菌落和心内膜炎，并伴有脾组织细胞增生。这是成功的针对少年Ballan濑鱼的As浴攻击模型的首次报道，该模型为疫苗效力和免疫能力的未来研究提供了重要的工具。