Resistance of Pseudomonas anguilliseptica to bactericidal action of fish serum.

Abstract

Resistance of an eel pathogen Pseudomonas anguilliseptica to bactericidal action of fish sera was compared between K antigen-possessing (K+) and -lacking (K-) strains in connection with their pathogenicity. The K+ strain displayed high resistance to the bactericidal action of Japanese eel, European eel, and bluegill sera, but not to carp, goldfish, rainbow trout, or tilapia sera, whereas the K- strain was highly sensitive to all sera. The pathogenicity tests proved that the former three species were susceptible to the virulent K+ strain, but the latter four were not. Thus, the K antigen-related resistance to serum-killing corresponded with the pathogenicity of the organism. The bactericidal activity of fish serum was more effective at 28°C than at 20°C, and was lost by heat-treatment at 50°C for 30 min.