Control of bacterial infections in cultured fish and shellfish by means or bacteriophages

噬菌体作为特异的病原菌杀灭剂被认为是控制鱼类细菌感染的有效药物，但对鱼类和贝类细菌感染的治疗和预防却鲜有人关注。本研究旨在探讨噬菌体疗法在水产养殖中应用的可能性，主要结果如下：1.在养殖的西洋参中，引起链球菌感染的致病菌是一种主要的噬菌体类型(噬菌体：链状病毒科)。当实验感染加维氏乳杆菌的鱼接受腹腔或口服抗L.与未投喂噬菌体的对照鱼相比，加毒噬菌体的鱼的死亡率显著降低。高山阿鱼细菌性出血性腹水的病原菌为单噬菌体(Myoviridae和Podoviridae)。口服噬菌体浸渍饲料提高了对舌疫霉菌实验感染的抵抗力。当噬菌体治疗在与先前感染了P.plecogolssicida的鱼共存的条件下进行评估时，接受噬菌体治疗的鱼的死亡率显著低于未处理的对照鱼。有趣的是，抗噬菌体变异体对AYU没有表现出毒力。一种田间噬菌体疗法显著降低了由P.plecogolssicida感染引起的阿育的死亡率。在整个田间治疗过程中，没有从鱼中检测到抗噬菌体的Plecogolssicida，也没有从鱼中检测到吞噬细胞抗体。用噬菌体治疗日本牡蛎幼虫感染太平洋弧菌生物群II也得到了类似的结果，但该病原菌的噬菌体类型(噬菌体：Podoviridae)并不是单一的，这些结果表明利用噬菌体来控制养殖现场的病害是可能的。

Bacteriophages (phages) as specific pathogen-killers are expected as agents for controlling fish bacterial infections, but little attention has been paid for phage therapy and prophylaxis of bacterial infections of fish and shellfish. The present study was conducted to examine a possibility of phage-therapy in aquaculture and results are summarized as follows:1. Lactococcus garvieae, the causative agent of streptococcal infection in cultured yellowtail Seriola quinqueradiata, consisted of a major phage type (phages : Siphoviridae). When experimentally infected fish with L. garvieae received intraperitoneally or orally administered anti-L. garvieae phages, fish showed significantly lower mortality compared with control fish without phage administrations2. Pseudomonas plecoglossicida, the causative agent of bacterial hemorrhagic ascites in cultured ayu Pleooglossus altivelis consisted of a single phage type (phages : Myoviridae and Podoviridae). Oral administration of phage-impregnated feed to ayu increased resistance against experimental infection with P. plecoglossicida. When phage-therapy was evaluated under cohabitation conditions with fish which had been previously infected with P. plecogolssicida, phage-received fish showed significantly lower mortality than that of untreated control fish. Interestingly, phage-resistant variants of P. plecogolssicida exhibited no virulence to ayu. A field phage therapy reduced markedly mortalities of ayu due to P. plecogolssicida infection. Throughout the field therapy, neither phage-resistant P. plecogolssicida were detected from fish, nor phageneutrahzing antibodies were detected from fish.3. Similar result was also obtained in phage-therapy experiments on Vibrio splendidus biovar II infection of larvae Japanese oyster Crassostrea gigas, though the phage type (phages : Podoviridae) of this pathogen was not single.These results suggest that it may be possible to use phages to control the diseases in the aquaculture field.