Högfors-Rönnholm Eva, Wiklund Tom
Laboratory of Aquatic Pathobiology, Department of Biology, Abo Akademi University, BioCity, Tykistökatu 6, 20520 Turku, Finland.
Dis Aquat Organ. 2010 May 18;90(1):43-53. doi: 10.3354/dao02211.
Four 'smooth' and 4 'rough' colony phenotypes of the Gram-negative fish pathogen Flavobacterium psychrophilum isolated from rainbow trout Oncorhynchus mykiss were characterized using biochemical, physiological, molecular and virulence tests to better understand the pathogenesis of the bacterium. Biochemically, the 2 cell types did not react significantly differently. Physiologically, the 2 phenotypes had distinct characteristics, and, when grown in broth, the smooth cells were found to be autoagglutinating and able to switch into the non-agglutinating rough phenotype. The rough cells did not switch into the smooth phenotype under any growth conditions tested, indicating that the phase variation from the smooth to rough phenotype is irreversible or that the conditions for the reversible switch are still to be found. Smooth cells were hydrophobic and more adhesive compared to the hydrophilic rough cells, suggesting that the phase variation most probably involves one or several surface structures other than outer membrane proteins and lipopolysaccharides that were found to be similar in both types. Analysis of extracellular products produced by the 2 cell types indicated furthermore that a difference in enzymatic activities could exist. Both cell types were virulent for rainbow trout in an intramuscular challenge; thus, the distinct physiological characteristics of the phenotypes do not seem to be directly associated with virulence, when the body surface of the fish is disregarded. The results suggest that phase variation occurs in F. psychrophilum, but that the importance of the 2 phenotypes for the pathogenesis of the bacterium has still to be investigated.
从虹鳟鱼（Oncorhynchus mykiss）中分离出的革兰氏阴性鱼类病原菌嗜冷黄杆菌（Flavobacterium psychrophilum）有4种“光滑”和4种“粗糙”菌落表型，通过生化、生理、分子和毒力试验对其进行了表征，以更好地了解该细菌的发病机制。在生化方面，这两种细胞类型的反应没有显著差异。在生理方面，这两种表型具有不同的特征，并且在肉汤中培养时，发现光滑细胞会自动凝集，并能够转变为不凝集的粗糙表型。在任何测试的生长条件下，粗糙细胞都不会转变为光滑表型，这表明从光滑表型到粗糙表型的相变是不可逆的，或者是仍有待发现可逆转变的条件。与亲水性的粗糙细胞相比，光滑细胞具有疏水性且更具粘附性，这表明相变很可能涉及除外膜蛋白和脂多糖之外的一种或几种表面结构，而这两种细胞类型中的外膜蛋白和脂多糖被发现是相似的。对这两种细胞类型产生的细胞外产物的分析进一步表明，酶活性可能存在差异。在肌肉注射攻毒试验中，这两种细胞类型对虹鳟鱼都具有毒性；因此，当不考虑鱼的体表时，这些表型的不同生理特征似乎与毒力没有直接关联。结果表明嗜冷黄杆菌会发生相变，但这两种表型对该细菌发病机制的重要性仍有待研究。
