The effect of oxytetracycline (OTC) treatment on intestinal bacterial populations in juvenile Atlantic salmon Salmo salar was evaluated. Oxytetracycline was administered by way of medicated feed to fish held in experimental tanks. Restriction fragment length polymorphism and sequencing of 16S rDNA from isolates were used to analyze the intestinal microbiota before, during, and after OTC administration. The microbiota from untreated fish was more diverse, consisting mainly of Pseudomonas, Acinetobacter, Bacillus, Flavobacterium, Psycrobacter, and Brevundimonas spp. In contrast, the microbiota of the OTC-treated group was characterized by lower diversity and consisted only of Aeromonas, clustering with A. sobria and A. salmonicida. Antibiotic-resistant isolates were identified as Aeromonas spp.; sequencing the resistance determinant showed it to be the tetE gene. Overall, OTC treatment changed the composition of the intestinal microbiota of Atlantic salmon, as evidenced by a reduction in bacterial diversity. These results support the current concern that antibiotic treatment can facilitate the proliferation of opportunistic bacteria by eradicating competing microorganisms.

中文翻译：

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土霉素处理降低大西洋鲑鱼肠道微生物群的细菌多样性

评估了土霉素 (OTC) 处理对大西洋鲑鲑鱼幼鱼肠道细菌种群的影响。土霉素通过药物饲料喂给实验水箱中的鱼。使用限制性片段长度多态性和分离株的 16S rDNA 测序来分析非处方药给药前、给药期间和给药后的肠道微生物群。未经处理的鱼的微生物群更加多样化，主要包括假单胞菌、不动杆菌、芽孢杆菌、黄杆菌、假杆菌和短杆菌属。相比之下，OTC 处理组的微生物群的特点是多样性较低，仅由气单胞菌组成，与 A. sobria 和 A. salicida 聚集在一起。耐抗生素分离株被鉴定为气单胞菌属；对抗性决定簇进行测序表明它是 tetE 基因。总体而言，OTC 治疗改变了大西洋鲑鱼肠道微生物群的组成，细菌多样性的减少证明了这一点。这些结果支持目前的担忧，即抗生素治疗可以通过根除竞争性微生物来促进机会性细菌的增殖。