Antibacterial activity of Phyllanthus amarus extracts towards hemorrhagic disease in Red drum (Sciaenops ocellatus) caused by Vibrio alginolyticus strains

Abstract

Red drum (Sciaenops ocellatus) is a valuable and widespread culture fish species in Vietnam. However, the hemorrhagic disease caused by V. alginolyticus is a major challenge for Red drum culture in Thua Thien Hue province. This study determined the antibacterial activity of the Phyllanthus amarus extracts against five V. alginolyticus strains causing the hemorrhagic disease in Red drum. The results show that the Phyllanthus amarus extracts at 100–500 mg/mL concentrations inhibit all strains of V. alginolyticus, with the concentration of 500 mg/mL being the most effective (p < 0,05). The minimum inhibitory concentration (MIC) ranged 6.25–25 mg/mL, and the minimum bactericidal concentration (MBC) ranged 25–50 mg/mL; the ratio of MBC/MIC of five tested strains is 2 to 4. The toxicity test indicated that the Phyllanthus amarus extracts at 50–2,000 mg/mL concentrations are also safe for fish at the fingerling stage.