Norwegian Veterinary Institute, P.O. Box 750 Sentrum, 0106 Oslo, Norway.
Vet Microbiol. 2013 Apr 12;163(1-2):133-41. doi: 10.1016/j.vetmic.2012.12.012. Epub 2012 Dec 20.
Saprolegnia spp. can cause mortality and economic losses in freshwater fish and eggs. Biofilm formation is generally regarded as a virulence factor, and biofilms can be an important cause of infection recurrence. Evidence of persistent sources of Saprolegnia infections on fish and eggs in fish farms support the assumption that Saprolegnia spp. might be able to form biofilms. In this study, we aimed to test the ability of Saprolegnia to form biofilms where it can survive, reproduce and resist different chemicals used for its control. Naturally formed biofilms were obtained from laboratory aquaria. Saprolegnia growth within these biofilms was demonstrated with light microscopy and confirmed by isolation. Isolates were identified morphologically and molecularly on the basis of ITS-sequences. Two isolates were identified as Saprolegnia parasitica, a species known to be highly pathogenic for fish, while the other belonged to S. australis. Selected Saprolegnia strains obtained from natural biofilms were then used to establish simple methods for in vitro induction of Saprolegnia biofilm. The ability of Saprolegnia isolates to form biofilms with subsequent production of infective motile zoospores within the biofilm was documented by light and confocal laser scanning microscopy. We demonstrate for the first time that isolates of S. parasitica and S. australis can form biofilm communities together with multiple microorganisms, wherein they grow and reproduce. It is therefore likely that natural biofilms constitute incessant Saprolegnia reservoirs in nature and aquaculture.
水霉属（Saprolegnia spp.）可导致淡水鱼类和鱼类卵死亡，并造成经济损失。生物膜的形成通常被认为是一种毒力因子，而生物膜可能是感染复发的一个重要原因。鱼类养殖场中鱼类和鱼类卵持续存在水霉感染的证据支持这样一种假设，即水霉属（Saprolegnia spp.）可能具有形成生物膜的能力。在本研究中，我们旨在测试水霉在能够生存、繁殖和抵抗用于控制其生长的不同化学物质的条件下形成生物膜的能力。从实验室水族箱中获得了天然形成的生物膜。通过光镜观察和分离证实了生物膜内水霉的生长。根据 ITS 序列对分离株进行形态和分子鉴定。鉴定出的两个分离株为寄生水霉（Saprolegnia parasitica），这是一种对鱼类高度致病的物种，而另一个则属于南方水霉（S. australis）。然后，从天然生物膜中获得的选定水霉菌株被用于建立体外诱导水霉生物膜的简单方法。通过光镜和共聚焦激光扫描显微镜记录了水霉分离株形成生物膜的能力，以及生物膜内随后产生感染性游动游动孢子的能力。我们首次证明，寄生水霉和南方水霉的分离株可以与多种微生物一起形成生物膜群落，在该群落中它们可以生长和繁殖。因此，天然生物膜很可能是自然界和水产养殖中持续存在的水霉库。
