Comparative Proteomic Analysis Between Virulent and Less Virulent Strains of Edwardsiella ictaluri Isolated from Ayu Plecoglossus altivelis

Outbreaks of disease caused by the infection of Edwardsiella ictaluri in ayu Plecoglossus altivelis have been reported in rivers in Japan since 2007. In this study, we performed comparative proteomic analysis between the virulent strain FPC1091 and the less virulent strain FPC1214 to identify virulence factors of E. ictaluri to ayu. In the experimental infection, cumulative mortalities of the ayu intraperitoneally injected with FPC1091 (1.2 × 107 CFU/fish) and FPC1214 (2.2 × 107 CFU/fish) were 100% and 26.7%, respectively. The genetic fingerprint profile of FPC1214 was identical to that of FPC1091 in the amplified-fragment length polymorphism (AFLP) analysis. The analysis of two-dimensional polyacrylamide gel electrophoresis and mass spectrometry between FPC1091 and FPC 1214 revealed 23 proteins that were either specific to or produced in greater amounts in the virulent strain FPC1091. These proteins included components of the type III and type VI secretion systems, and the proteins that seem to be involved in the resistance against oxidative stress by host phagocytic cells, suggesting that these proteins are the virulence factors of E. ictaluri to ayu.