Antimicrobial activity of Polygonum equisetiforme extracts and flavonoids

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Abstract
Methanol, hexane, aqueous and petroleum ether extracts of the whole plant Polygonum equisetiforme did not show any activity against ten bacterial and four fungal species. The butanol crude extract and all the pooled groups of this exhibited variable patterns of antimicrobial activity. Quercetin (a flavonol) has been isolated and identified as the major constituent. The antifungal and antibacterial activity of quercetin was compared with the antibacterial drugs gentamycin, streptomycin and ampicillin and the antifungal drug miconazole nitrate. The antifungal activity of quercetin was limited to Candida tropicalis and it had a narrow antibacterial spectrum of activity. However, its activities against Enterobacter aerogenes and Escherichia coli were low grade compared with ampicillin, stretomycin and gentamycin. Quercetin‐3‐O‐rhamnoside, quercetin‐3‐O‐glucuronide, quercetin‐3‐O‐arabinoside and isorhamnetin were also isolated in very low yield. They have not been reported previously in this species.