The aim of this study was to demonstrate the presence of Flavobacterium psychrophilum in the west Aegean region of Turkey and to evaluate the in vitro susceptibility of F. psychrophilum (isolated from the fry of rainbow trout Oncorhynchus mykiss) to seven antimicrobial agents, as determined by the disk diffusion and agar dilution methods. A total of 250 rainbow trout fry (weight = 2-5 g; total length = 3-6 cm) were examined, and 20 bacterial isolates were phenotypically identified. Antimicrobial agents included in this investigation were amoxicillin-clavulanic acid (AMC), erythromycin (E), enrofloxacin (ENR), florfenicol (FFC), gentamicin (CN), oxytetracycline (OT), and sulfamethoxazole-trimethoprim (SXT). Disk diffusion and agar dilution methods were performed according to published standards. Minimum inhibitory concentration (MIC) ranges were determined using the agar dilution method for F. psychrophilum isolates. Resistance of F. psychrophilum to CN (disk diffusion method: 70%; agar dilution method: 95%), E (65%; 100%), and SXT (75%; 100%) was high using both methods. Resistance to ENR (10%; 15%) and FFC (25%; 25%) was low with both methods; MIC90 (minimum concentration required to inhibit bacterial growth by 90%) was 4 microg/mL for ENR and 16 microg/mL for FFC. Ninety percent of the F. psychrophilum isolates were resistant to AMC based on the disk diffusion method, while only 15% of isolates showed resistance based on the agar dilution method. For OT, 20% of isolates were resistant based on disk diffusion, while 75% exhibited resistance based on agar dilution. The importance of susceptibility testing when facing an outbreak of F. psychrophilum at a fish farm is obvious; however, the discrepancies between testing methods for AMC and OT require further studies.

中文翻译：

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虹鳟鱼苗分离嗜冷黄杆菌体外抗菌药物敏感性比较

本研究的目的是证明在土耳其爱琴海西部地区存在 Flavobacterium psychrophilum 并评估 F. psychrophilum（从虹鳟 Oncorhynchus mykiss 鱼苗中分离出来）对七种抗菌剂的体外敏感性，由以下方法确定圆盘扩散法和琼脂稀释法。检查了总共 250 条虹鳟鱼苗（重量 = 2-5 克；总长度 = 3-6 厘米），并通过表型鉴定了 20 个细菌分离株。本次调查的抗菌药物包括阿莫西林-克拉维酸 (AMC)、红霉素 (E)、恩诺沙星 (ENR)、氟苯尼考 (FFC)、庆大霉素 (CN)、土霉素 (OT) 和磺胺甲恶唑-甲氧苄啶 (SXT)。圆盘扩散和琼脂稀释方法根据已公布的标准进行。最低抑菌浓度 (MIC) 范围使用琼脂稀释法测定嗜冷嗜热菌分离物。F. psychrophilum 对 CN（圆盘扩散法：70%；琼脂稀释法：95%）、E（65%；100%）和 SXT（75%；100%）的抗性在使用这两种方法时都很高。两种方法对 ENR (10%; 15%) 和 FFC (25%; 25%) 的抗性都很低；ENR 的 MIC90（抑制细菌生长 90% 所需的最低浓度）为 4 微克/毫升，FFC 为 16 微克/毫升。根据圆盘扩散法，90% 的嗜冷杆菌分离株对 AMC 具有抗性，而根据琼脂稀释法，只有 15% 的分离株显示出抗性。对于 OT，20% 的分离株对磁盘扩散具有抗性，而 75% 的分离株表现出基于琼脂稀释的抗性。面临 F. 爆发时药敏试验的重要性。养鱼场的嗜冷菌很明显；然而，AMC 和 OT 测试方法之间的差异需要进一步研究。