A lytic bacteriophage of the newly emerging rainbow trout pathogen Weissella ceti

This study was conducted to isolate and characterize a bacteriophage of a newly emerging pathogen, Weissella ceti, which causes weissellosis outbreaks of intensively farmed rainbow trout worldwide. The phage appeared together with the cultured Weissella ceti during isolation of pathogen from kidney of diseased rainbow trout. The morphological, physiological, proteomic and lytic spectrum were characterized. This phage, named PWc, belonged to the family Siphoviridae and possessed an isometric head (approximately 65 nm in diameter) and a flexible, non-contractile tail of 170-180 nm in length. The latent time and burst size of PWc were approximately 25 min and 16 PFU/infected cells, respectively. The PWc was relatively stable over a wide range of temperatures and pH values and possessed a broad lytic spectrum, lysing all 36 tested W. ceti strains isolated from diseased rainbow trout in Japan. The protein profile of the phage was obtained using SDS-PAGE analysis, and the potential packaging strategy was determined based on terminase large subunit sequence analysis. This is the first study to investigate a lytic bacteriophage of a newly emerging pathogen W. ceti that causes infectious disease in rainbow trout.