Surveillance of antibiotic resistance is of paramount importance for animal welfare and production. Despite aquaculture being a main source of animal protein, studies on antibiotic susceptibility in fish pathogens are scarce. Renibacterium salmoninarum, the aetiological agent of bacterial kidney disease (BKD), is one of the most common bacterial pathogens affecting salmon farming. In this work, we present an analysis of susceptibility patterns using determinations of minimum inhibitory concentration (MIC) for 65 field isolates, which were collected over seven years (2013–2019) from Atlantic salmon (Salmo salar) and coho salmon (Oncorhynchus kisutch) farms across southern Chile. The MIC protocol described by the Clinical Laboratory Standards Institute (CLSI) was used, but with microdilution instead of macrodilution and eight instead of four days of incubation. Two laboratories independently conducted analyses to provide data on the epidemiological cut‐off values for R. salmoninarum to florfenicol, oxytetracycline and erythromycin. By using two calculation methods, our results provide evidence for an evolving subpopulation of non‐wild‐type isolates for the macrolide erythromycin, which is consistent with the respective treatment frequencies prescribed against BKD. Contrasting with what was expected, R. salmoninarum isolates were most susceptible to florfenicol and oxytetracycline, both of which are widely used antibiotics currently used in the Chilean salmon industry. The presented findings can serve as a reference for national or international antibiotic surveillance programmes, for both MIC interpretation and to identify emerging resistance to the conventional drugs used in BKD management. Finally, our results indicate that an 8‐day incubation period for establishing MIC values of R. salmoninarum should be considered in a future revision of the CLSI guidelines.

中文翻译：

---

在智利鲑鱼养殖场进行MIC检测以确定沙门氏菌的抗菌敏感性的拟议方案

监测抗生素抗性对于动物的福利和生产至关重要。尽管水产养殖是动物蛋白的主要来源，但对鱼类病原体中抗生素敏感性的研究却很少。鲑鱼肾杆菌是细菌性肾脏病（BKD）的病原学，是影响鲑鱼养殖的最常见细菌病原体之一。在这项工作中，我们通过测定65种野外分离株的最小抑菌浓度（MIC）进行敏感性分析，这些分离株是在7年（2013-2019）期间从大西洋鲑（Salmo salar）和银鲑（Oncorhynchus）收集的kisutch）遍布智利南部的农场。使用了由临床实验室标准协会（CLSI）描述的MIC方案，但用微量稀释代替了宏观稀释，并用了八天而不是四天的孵育时间。两个实验室独立进行分析，以提供有关沙门氏菌到氟苯尼考，土霉素和红霉素的流行病学临界值的数据。通过使用两种计算方法，我们的结果提供了大环内酯类红霉素非野生型分离株不断发展的亚群的证据，这与针对BKD规定的相应治疗频率一致。与预期的相反，鲑鱼分离株对氟苯尼考和土霉素最敏感，这两种都是目前智利鲑鱼业广泛使用的抗生素。提出的发现可作为国家或国际抗生素监测计划的参考，既可用于MIC的解释，也可用于确定对BKD管理中使用的常规药物的新耐药性。最后，我们的结果表明，在将来修订CLSI指南时，应考虑8天的潜伏期以确定沙门氏菌的MIC值。