Detection and characterization of Aeromonas salmonicida subsp. salmonicida infection in crucian carp Carassius auratus.

Aeromonas salmonicida is one of the most important pathogens in salmonids and non-salmonids species. Nevertheless, very little was reported in cyprinids about A. salmonicida infection. Hence, a pathogenic A. salmonicida subsp. salmonicida, namely isolate GCA-518, was isolated from diseased crucian carp Carassius auratus. Its optimal growth conditions were at 28 °C, pH 7.0 and 1.5% NaCl. Furthermore, the quantitative real-time PCR (qPCR) targeting serine protease (aspA) gene was established for rapid detection of the lowest limit of 5.6 × 102 copies per reaction. The pathogenicity was confirmed in crucian carp by intraperitoneal infection. Histopathologic examination displayed multifocal necrosis and infiltration of inflammatory cells in gill, liver, kidney and intestine. This is the first report on typical A. salmonicida infection in cultured crucian carp.