Francisella orientalis (Fo) is considered to be one of the major pathogens of tilapia because of the high mortalities observed during outbreaks. Other cichlids belonging to the same family (Cichlidae) as tilapia are also quite susceptible to this pathogen. On various occasions, Fo has also been isolated from other warm water fish, including three-line grunt, hybrid striped bass, French grunt, Caesar grunt, and Indo-Pacific reef fish. However, only a few studies have reported the pathogenicity of Francisella orientalis in ornamental cichlid fish. This study fulfills Koch’s postulates by showing that a strain of Fo obtained from green Texas cichlid (Herichthys cyanoguttatus) was able to produce the same pathogenicity in healthy fish. A mortality of 100% was observed after healthy green Texas cichlid were experimentally injected with Fo at a dose of 8.95 × 10⁵ CFU/fish. DNA extracted from the organs of predilection (spleen, head kidney) gave positive results by PCR for all fish that died during the experimental period. Spleen and head kidney presented with multifocal white nodules in the affected fish, corresponding to typical vacuolated granulomas on histopathological examination of the tissues. Based on the results of this study, it is evident that Fo can indeed infect green Texas cichlid and produce a disease typical of francisellosis.

中文翻译：

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绿色德克萨斯慈鲷（Herichthys cyanoguttatus）中东方弗朗西斯氏菌的病理表现

Francisella orientalis ( Fo ) 被认为是罗非鱼的主要病原体之一，因为在爆发期间观察到的死亡率很高。与罗非鱼属于同一科（慈鲷科）的其他慈鲷也对这种病原体非常敏感。在各种场合，Fo也与其他温水鱼分离，包括三线鮟鱇鱼、混合条纹鲈鱼、法国鰤鱼、凯撒鰤鱼和印度太平洋礁鱼。然而，仅有少数研究报道了东方弗朗西斯氏菌对观赏慈鲷鱼的致病性。这项研究表明，从绿色德克萨斯慈鲷 ( Herichthys cyanoguttatus) 中获得的Fo菌株符合 Koch 的假设) 能够在健康鱼中产生相同的致病性。在以 8.95 × 10 ⁵ CFU/条鱼的剂量对健康的绿色德克萨斯慈鲷进行实验性注射Fo后，观察到 100% 的死亡率。从嗜好器官（脾脏、头肾）中提取的 DNA 通过 PCR 对所有在实验期间死亡的鱼都给出了阳性结果。脾脏和头肾在受影响的鱼中呈现多灶性白色结节，对应于组织的组织病理学检查中典型的空泡肉芽肿。根据这项研究的结果，很明显，Fo确实可以感染绿色德克萨斯慈鲷并产生一种典型的弗朗西氏菌病。