Antibacterial and antifungal activity of extracts and quercetagetin derivate isolated from Centaurea rupestris L. (Asteraceae)

The antibacterial and antifungal activity of Centaurea rupestris L. ethanolic and etheric leaf and inflorescence extracts and of quercetagetin 3'-methyl ether 7-O-beta-D glucopyranoside isolated from inflorescences was investigated. Inflorescence extract in 45% ethanol showed significant antifungal activity against the dermatophytes Epidermophyton floccosum, Microsporium gypseum and Trichophyton mentagrophytes (fungicidal zones between 18 and 23 mm, minimum fungicidal concentration 5-7%). The same extract showed weak bactericidal acitvity against Bacillus anthracis (bactericidal zone 9 mm, minimun bactericidal concentration 90%). In contrast, leaf extract in 90% ethanol possessed significant bactericidal activity against streptococcus faecalis (bactericidal zone 23 mm, minimum bactericidal concentration 9%). The antimicrobial spectrum of quercetagetin was broad but weak for G- bacteria and moderate for dermatophytes. Namely, it showed antibacterial activity against Klebsiella pneumoniae, Escherichia coli, Salmonella java and Serratia sp. (bactericidal zones 10 mm, minimum bactericidal concentration 5-6 mg/ml). The fungicidal zones created by quercetagetin against the dermatophytes Epidermophyton floccosum, Trichophyton mentagraphytes and Microsporum gypseum ranged from 14 to 18 mm (minimun fungicidal concentrations 3 mg/ml).