Relationship between in vitro motility of Pseudomonas plecoglossicida and clinical conditions in affected ayu

Abstract

This study was conducted to verify the previous contrasting results on the motility of Pseudomonas plecoglossicida and clinical conditions (bloody ascites) in affected ayu Plecoglossus altivelis. In the present field surveys at Tokushima Prefecture in 1999 and 2001, all P. plecoglossicida isolates from dead ayu, except one isolate from a fish with ascites, were non-motile irrespective of the presence of bloody ascites. When ayu were injected intramuscularly with nonmotile strains, either motile or non-motile isolates were obtained from the kidney of dead fish, while only motile ones were isolated after injection of motile strains. Bloody ascites manifested in most of the affected fish after injection of either type of the bacterium. In in vitro broth culture conditions, the non-motile strains altered into motile ones during two-week incubation. These results indicate that there are no relationship between in vitro motility of P. plecoglossicida and the presence of bloody ascites in affected ayu, and that the phenotypic alteration in the motility of P. plecoglossicida occurs under both in vitro and in vivo conditions.