Abstract：
This study aimed to identify and characterize isolates of Francisella salimarina associated with an outbreak on a marine fish farm in Brazil and to analyse their genetic variability and antimicrobial susceptibility. In 2021, diseased cobias (Rachycentron canadum, n = 10) and dusky groupers (Epinephelus marginatus, n = 10) were sampled and subjected to bacteriological and pathological examinations. The isolates obtained were morphologically and biochemically characterized and identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-ToF) and 16S rRNA gene sequencing. The genetic diversity of these isolates was analysed using repetitive extragenic palindromic-polymerase chain reaction (REP-PCR). Antimicrobial susceptibility was assessed using the disk diffusion technique. Macroscopically, the fish presented skin ulcerations, ocular lesions, hepatomegaly and splenomegaly. A pleomorphic, gram-negative, catalase- and oxidase-positive bacterium was isolated from seven cobias and two groupers. The 16S rRNA gene sequences showed >99% coverage and identity with other deposited sequences of F. salimarina. The results of the biochemical analysis corresponded to these bacterial species. Histologically, granulomas were observed in the spleen, liver and heart of the cobias (n = 6), and necrotizing and fibrinous dermatitis and myositis were identified in some groupers (n = 2). The isolates exhibited the same banding pattern when REP-PCR was performed, indicating that they were clonally related. Finally, the antibiogram test, no inhibition halo was observed for amoxicillin and trimethoprim-sulfamethoxazole. To our knowledge, this is the first report of F. salimarina infection in cobias and dusky groupers.
摘要：
这项研究旨在鉴定和表征与巴西海鱼场爆发有关的Francisellasalimarina分离株，并分析其遗传变异性和抗菌敏感性。2021年，患病的cobias(Rachycentroncanadum，n=10）和暗淡的石斑鱼（石斑鱼，n=10）取样并进行细菌学和病理学检查。通过基质辅助激光解吸/电离飞行时间（MALDI-ToF）和16SrRNA基因测序对获得的分离株进行了形态学和生物化学表征和鉴定。使用重复的基因外回文聚合酶链反应（REP-PCR）分析了这些分离株的遗传多样性。使用圆盘扩散技术评估抗菌药物敏感性。宏观上,鱼出现皮肤溃疡，眼部病变,肝肿大和脾肿大。多形性，革兰氏阴性,从七个cobias和两个石斑鱼中分离出过氧化氢酶和氧化酶阳性细菌。16SrRNA基因序列显示>99%的覆盖率,并且与沙利马利纳的其他保藏序列相同。生化分析的结果对应于这些细菌物种。组织学上,在脾脏中观察到肉芽肿，cobias的肝脏和心脏(n=6)，在一些石斑鱼中发现了坏死性和纤维蛋白性皮炎和肌炎（n=2）。进行REP-PCR时，分离株表现出相同的条带模式，表明它们是克隆相关的。最后,抗菌谱测试，阿莫西林和甲氧苄啶-磺胺甲恶唑未观察到抑制晕.据我们所知,这是在cobias和昏暗的石斑鱼中首次报道F.salimarina感染。
