Bioassay-directed Isolation and Evaluation of Harmine from the Terrestrial Plant Peganum harmala L. for Antibacterial Activity against Flavobacterium columnare

摘要

Enteric septicemia of catfish (ESC) and columnaris disease in pond-raised channel catfish (Ictalurus punctatus ) are caused by Edwardsiella ictaluri and Flavobacterium columnare , respectively, while Streptococcus iniae can cause streptococcosis in freshwater fish. During our search for natural compounds to replace antibiotics used to manage these diseases, the antibacterial activities of crude extracts obtained from the aerial portions and roots of Peganum harmala L. were evaluated against these common fish pathogenic bacteria species using a rapid bioassay. The ethanol extract of the roots of P. harmala was found to be the most active against F. columnare , with a 50% inhibition concentration (IC_(50)) of 16 mg/L and a minimum inhibition concentration (MIC) of 10.0 mg/L. Bioassay-guided fractionation of this extract resulted in the isolation of harmine (7-methoxy-1-methyl-9H-pyrido[3,4-b] indole) as the active compound, with an IC_(50) of 3.8 mg/L and MIC of 10.0 mg/L. Harmine appears to be promising for evaluation of toxicity towards channel catfish and for efficacy studies to determine its potential use in managing columnaris disease in pond-raised channel catfish.