Further Study on Serotyping of Flavobacterium psychrophilum.

Flavobacterium psychrophilum (syn. Cytophaga psychrophila) is the causative agent of bacterial cold water disease (BCWD)1,2). In Japan, since the middle of the 1980's, BCWD has predominantly affected fry and fingerlings of coho salmon (Oncorhynchus kisutch) in hatcheries, and in recent years the disease has also spread among cultured and wild ayu (Plecoglossus altivelis) and other host species3-5). For the thermostable antigens two distinct serotypes of F. psychrophilum from different host species (O-1 and O-2) have already been determined by microtiter method. Serotype O-1 was found in strains from coho salmon in Japan and the USA. Strains from ayu belonged to serotype O-2. However, an untypable serotype was recognized in some strains from rainbow trout (O. mykiss, provisionally categorized to serotype O -2)4).