Use of PCR to detect Cytophaga psychrophila from apparently healthy juvenile ayu and coho salmon eggs

The nested PCR was used to detect Cytophaga psychrophila carried by juvenile ayu (Plecoglossus altivelis) and eyed eggs of coho salmon (Oncorhynchus kistch). Ayu juveniles were caught in Lake Biwa and frozen shortly after landed. The coho salmon eggs from the USA and Japan were collected on a lot-by-lot basis at Narita airport or hatcheries when the containers arrived. Chelex 100 was used as a medium for extraction of DNA from these samples. Utilizing the PCR, a specific primer pair of PSY1 and PSY2 for C. psychrophila was used to amplify its 16S rDNA segments. An amplification product of the expected size was obtained from 5 of 24 DNA extractions from the kidney of ayu samples in April 1995. These fish had been previously diagnosed as negative for the presence of C. psychrophila by cultivation on TYE agar and IFAT. Five of 11 lots of coho salmon eggs were found to be positive for C. psychrophila by PCR. Four of these five lots had also been diagnosed as positive by cultivation and IFAT. In addition, the sensitivity of the PCR amplification for detecting C. psychrophila in kidney samples of ayu was calculated to be 1.5 CFU per PCR reaction tube.