Antimicrobial activity of extract and two alkaloids from traditional Chinese medicinal plant Stephania dielsiana

Two alkaloids, stephanine and crebanine, were isolated from tubers of the traditional Chinese medicinal plant Stephania dielsiana, using an activity-directed isolation method, and inhibitory activity of methanol extract, stephanine and crebanine against ten animal pathogenic bacteria and eight plant pathogenic fungi was evaluated in vitro. The results showed that extract from S. dielsiana exhibited high inhibitory activity against five gram-positive and four gram-negative animal pathogenic bacteria, with MIC values of 0.625–7.5 g/l; stephanine and crebanine had high inhibitory activity against gram-positive animal pathogenic bacteria, with MIC values of 0.078–0.312 g/l, but low inhibitory activity against gram-negative animal pathogenic bacteria. Methanol extract, stephanine and crebanine also inhibited hyphal growth of the plant pathogens Cercospora kaki, Gymnosporangium haraeanum, Pyricularia oryzae, Rhizoctonia solani and Colletotrichum graminicola, and spores germination of Thielaviopsis paradoxa, Fusarium oxysporum f. sp. niveum, Sphaceloma fawcettii and G. haraeanum.