Antibacterial and antifungal activities of six plant-derived flavonoids representing two different structural groups were evaluated against standard strains of Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and their drug-resistant isolates, as well as fungi (Candida albicans, C. krusei) using the microdilution broth method. Herpes simplex virus Type-1 and Parainfluenza-3 virus were employed for antiviral assessment of the flavonoids using Madin-Darby bovine kidney and Vero cell lines. Ampicillin, gentamycin, ofloxacin, levofloxacin, fluconazole, ketoconazole, acyclovir, and oseltamivir were used as the control agents. All tested compounds (32-128 mu g/ml) showed strong antimicrobial and antifungal activities against isolated strains of P aeruginosa, A. baumanni, S. aureus, and C. krusei. Rutin, 5,7-dimethoxyflavanone-4'-O-beta-D-glucopyranoside and 5,7,3'-trihydroxy-flavanone-4'-O-beta-D-glucopyranoside (0.2-0.05 mu g/ml) were active against Pl-3, while 5,7-dimethoxyflavanone-4'-O-[2 ''-O-(5'''-O-trans-cinnamoyl)-beta-D-apiofuranosyl]-beta-D-glucopyranoside (0.16-0.2 mu g/ml) inhibited potently HSV-1. (C) 2009 Elsevier GmbH. All rights reserved.