Antibacterial activities of bark extracts from Fraxinus rhynchophylla Hance and Geranium koreanum Kom. Against clinical strains of Clostridium perfringens in chickens

Necrotic enteritis (NE) caused by Clostridium (C.) perfringens commonly occurs in domestic broiler farms since antibiotic supplementation in poultry feed has been banned. We evaluated the antibacterial activities of medicinal plant extracts against C. Perfringens isolates to select alternative compounds for preventing NE. We compared antibacterial activities using two methods and evaluated susceptibilities of the isolates based on minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Two (Fraxinus rhynchophylla Hance [FRH] and Geranium koreanum Kom. [GKK]) of the 30 plant extracts had potent antibacterial activities against C. Perfringens ATCC 13124 in two assays. The MIC values for FRH and GKK against 20 C. Perfringens isolates were 128~256 μg/mL and 32~128 μg/mL, respectively. The geometric MIC mean values for the two extracts were 147.2 μg/mL and 68.8 μg/mL, respectively. The MBCs for the two extracts against the same strains were 1,024~2,048 μg/mL and 256~1,024 μg/mL, respectively. The geometric mean MIC and MBC for GKK were about two-fold lower than those of FRH. The modified spot-on-lawn assay may be useful for measuring primary antibacterial potential. FRH and GKK are expected to be used as feed additives to prevent or treat NE in veterinary practice.