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

噬菌体作为一种特殊的病原体杀伤剂，有望成为控制鱼类细菌感染的药物，但对鱼类和贝类细菌感染的噬菌体治疗和预防却很少受到重视。本研究旨在探讨噬菌体治疗在水产养殖中的可能性，研究结果总结如下：1。鸡乳球菌（Lactococcus garvieae）是引起五角黄尾Seriola quinqueradiata链球菌感染的病原体，由一种主要的噬菌体类型（噬菌体：Siphoviridae）组成。当实验感染了鸡乳杆菌的鱼接受腹腔或口服抗鸡乳杆菌。与未注射噬菌体的对照鱼相比，经Garvieae噬菌体感染的鱼死亡率显著降低。羊舌假单胞菌（Pseudomonas plecloglossicida）是引起羊舌细菌出血性腹水的病原菌，由单一噬菌体类型组成（噬菌体：肌病毒科和足病毒科）。口服噬菌体浸渍饲料可提高阿育鱼对棘球绦虫实验感染的抵抗力。当噬菌体治疗与先前感染过P. plecogolssicida的鱼同居时进行评估时，接受噬菌体治疗的鱼的死亡率显着低于未经治疗的对照鱼。有趣的是，耐噬菌体变异的plecogolssicida对ayu没有毒力。野外噬菌体治疗可显著降低因pplecogolssicida感染而导致的ayu死亡率。在整个现场治疗过程中，未在鱼体中检测到耐噬菌体P. pleecogossicida，也未在鱼体中检测到抗噬菌体抗体。在侵染日本牡蛎长牡蛎幼虫的脾弧菌II型生物变种的噬菌体治疗实验中也得到了类似的结果，尽管该病原菌的噬菌体类型（噬菌体：足病毒科）并不单一。这些结果表明，利用噬菌体对水产养殖场的病害进行控制是可能的。

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.