BACKGROUND Renibacterium salmoninarum and Mycobacterium sp. are important bacterial pathogens of fish. R. salmoninarum is the causative agent of bacterial kidney disease, a Gram-positive bacterium mostly known for causing chronic infections in salmonid fish, while multiple species belonging to the Mycobacterium genus have been associated with mycobacteriosis in fish as well as in human. The objective of this study was to determine the prevalence of these two bacterial pathogens in populations of wild brown trout (Salmo trutta fario) in four rivers (Kamp, Wulka, Traun and Ybbs) in Austria. RESULTS A total of 457 kidney samples were examined for both bacterial agents using nested and conventional PCR as well as bacterial cultivation on KDM-2, histological examination and immunohistochemistry. Molecular evidence showed an estimated prevalence level of 0.94% for R. salmoninarum in 2017 while the bacterium could not be detected in 2018 and histology showed signs consistent with a low-level chronic inflammation in the kidney of infected fish. Similarly, no fish were found positive for Mycobacterium in 2017 but in 2018, the prevalence was found to be 37.03% in the Kamp river (4.08% across all rivers). The sequencing data confirmed that these fish carried Mycobacterium sp. although the precise species of Mycobacterium could not be ascertained. CONCLUSIONS This survey constitutes the first insight into the prevalence rate of R. salmoninarum and Mycobacterium sp. in wild brown trout (Salmo trutta fario) populations in Austria. Both of these pathogens were only detected in the summer months (June and July), which might suggest that the stress linked to increased water temperature could act as stressor factor and contribute to the outbreak of these diseases. The age of the fish might also play a role, especially in the case of Mycobacterium sp. as all the infected fish were in their first summer (June).

中文翻译：

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鲑鱼肾杆菌和分枝杆菌：两种细菌病原体在奥地利河流中的野生褐鳟（Salmo trutta fario）种群中含量较低。

背景鲑鱼肾杆菌和分枝杆菌。是鱼类重要的细菌性病原体。鲑鱼罗氏杆菌是细菌性肾病的病原体，这是一种革兰氏阳性细菌，主要因引起鲑鱼慢性感染而闻名，而属于分枝杆菌属的多种物种与鱼类和人类的分枝杆菌病有关。本研究的目的是确定这两种细菌病原体在奥地利四条河流（坎普河、乌尔卡河、特劳恩河和伊布斯河）野生褐鳟鱼（Salmo trutta fario）种群中的流行情况。结果 使用巢式和常规 PCR 以及 KDM-2 上的细菌培养、组织学检查和免疫组织化学检查了总共 457 个肾脏样本的细菌制剂。分子证据显示，2017 年鲑鱼红鲑鱼的患病率估计为 0.94%，而 2018 年无法检测到这种细菌，组织学显示的迹象与受感染鱼的肾脏存在低水平慢性炎症一致。同样，2017 年没有发现鱼类分枝杆菌呈阳性，但 2018 年，坎普河的患病率为 37.03%（所有河流为 4.08%）。测序数据证实这些鱼携带分枝杆菌。尽管分枝杆菌的确切种类无法确定。结论 这项调查首次深入了解了鲑鱼红藻和分枝杆菌的流行率。奥地利野生褐鳟鱼 (Salmo trutta fario) 种群中。这两种病原体仅在夏季（六月和七月）被发现，这可能表明与水温升高相关的压力可能作为压力因素并导致这些疾病的爆发。鱼的年龄也可能发挥作用，特别是对于分枝杆菌而言。因为所有受感染的鱼都处于第一个夏天（六月）。