Antimicrobial activities of eucalyptus leaf extracts and flavonoids from Eucalyptus maculata

Aims: We investigated the antimicrobial activities of eucalyptus leaf extracts to find effective antibacterial agents. Methods and Results: The antimicrobial activities of leaf extracts from 26 species of eucalyptus were measured. Extracts of Eucalyptus globulus, E. maculata and E. viminalis significantly inhibited the growth of six Gram-positive bacteria (Staphylococcus aureus, MRSA, Bacillus cereus, Enterococcus faecalis, Alicyclobacillus acidoterrestris, Propionibacterium acnes), and of a fungus (Trichophyton mentagrophytes), but they did not show strong antibacterial activity against Gram-negative bacteria (Escherichia coli, Pseudomonas putida). 2',6'-dihydroxy-3'-methyl-4'-methoxy-dihydrochalcone, eucalyptin and 8-desmethyl-eucalyptin, isolated from E. maculata extracts, exhibited potent antimicrobial activities against seven micro-organisms with minimum inhibitory concentrations (MIC) ranging from 1.0 to 31 mg l(-1). Conclusions: The eucalyptus extracts and three compounds from E. maculata were found to be effective against micro-organisms that cause food poisoning, acne and athlete's foot. Significance and Impact of the Study: This study shows potential uses of extracts from E. globulus, E. maculata and E. viminalis, and antimicrobial compounds isolated from E. maculata.