Antimicrobial Activity of Eucalyptus major and Eucalyptus baileyana Methanolic Extracts

The antimicrobial activity of methanolic extracts of Eucalyptus baileyana leaves and Eucalyptus major leaves and flowers were investigated by disc diffusion assay against a panel of bacteria and fungi. E. baileyana leaf extract inhibited the growth of 6 of the 14 bacteria tested (43%). Gram-positive and Gram-negative bacteria were both inhibited by E. baileyana leaf extract although Gram-positive bacteria were more susceptible. 4 of 11 Gram-negative (36%) and 2 of 3 Gram-positive bacteria (67%) had their growth inhibited by E. baileyana extract. E. major leaf extract displayed broad antibacterial activity, inhibiting the growth of 10 of the 14 bacteria (71%). E. major flower extract inhibited the growth of 7 of the 14 bacteria (50%). E. major leaf and flower extracts both preferentially inhibited Gram-positive bacteria (100%) compared to Gram-negative bacteria (64% inhibition by leaf extract; 36% inhibition by flower extracts). None of the Eucalyptus extracts showed any antifungal activity. The antibacterial activity of E. major leaf extract was further investigated by growth time course assays which showed significant growth inhibition in cultures of Bacillus cereus and Pseudomonas fluorescens within 1 h and in Bacillus subtilis and Aeromonas hydrophilia within 2 h.