Potential of (-)-epigallocatechin-3-gallate against bacterial and viral pathogens isolated from gibel carp (Carassius auratus gibelio)

Abstract

Gibel carp (Carassius auratus gibelio) is an important fish species cultured worldwide. Bacterial septicemia and herpesviral hematopoietic necrosis disease (HVHND) were caused by Aeromonas hydrophila and cyprinid herpesvirus 2 (CyHV-2) respectively, which were the main causes of mortality and economical loss in gibel carp production. With known pharmacological activities against certain gram-negative bacteria and herpesvirus, (−)-Epigallocatechin-3-gallate (EGCG) was tested here to evaluate its inhibitory activity against A. hydrophila and CyHV-2 pathogens isolated from gibel carp. The minimum inhibitory concentration (MIC) of EGCG against four A. hydrophila strains ranged from 256 to 512 μg/mL and the minimum bactericidal concentration (MBC) was determined to be 1024 μg/mL. The growth curves of A. hydrophila A56 in the presence of various amounts of EGCG indicated that the concentration and treatment time of EGCG served as the two dominant factors for EGCG-mediated inhibitory effects in vitro. The bacterial load in liver, spleen and kidney tissues of gibel carps infected with 0.1 × LD50 A56 was significantly reduced after oral administration of EGCG (40 mg/kg body weight) 8 h in advance. The inactivation effect of CyHV-2 virus treated with 50 μg/mL EGCG for 2 h could reach 99.99%, and 70 μg/mL of EGCG could completely inactivate CyHV-2 in our infection and inhibition assays in vitro. These results collectively revealed the potential and broad-spectrum useage of EGCG in gibel carp cultivation against either bacterial or viral pathogen.