Antibacterial Activity of Constituents from Mangosteen Garcinia mangostana Fruit Pericarp against Several Channel Catfish Pathogens

Bacterial diseases cause major financial damage to the producers of Channel Catfish Ictalurus punctatus in the southeastern USA . The two most common bacterial diseases among pond‐raised Channel Catfish are enteric septicemia of catfish, caused by the gram‐negative bacterium Edwardsiella ictaluri , and columnaris disease, caused by the rod‐shaped, gram‐negative bacterium Flavobacterium columnare . Streptococcosis is another, less‐common bacterial disease in catfish and is caused by the gram‐positive coccus Streptococcus iniae . Catfish farmers typically rely on commercial antibiotics and other chemicals to prevent the economic damage from these diseases. Environmentally benign and efficacious alternatives to the currently used antibiotics and chemicals will tremendously help the catfish aquaculture industry. As part of our ongoing efforts in the search for such novel compounds, we investigated ethyl acetate and methanol extracts of mangosteen Garcinia mangostana fruit pericarp via bioassay‐guided fractionation. Gamma‐mangostin (γ‐mangostin) was isolated and identified as the most promising active metabolite against F. columnare . One of the constituents in the mangosteen fruit pericarp, alpha‐mangostin (α‐mangostin), is the major xanthone; α‐mangostin was found to be 10‐fold less active than γ‐mangostin when minimum inhibitory concentration values were compared.