The in vitro antibacterial activity of essential oils from six plants was verified through minimal inhibitory concentration (MIC=%v/v), determined by diluting the oils in culture medium Mueller Hinton Agar, against Staphylococcus aureus (n=16) and Escherichia coli (n=16) strains isolated from human clinical specimens, besides one standard ATCC strain for each species (Sa 25923 and Ec 25922). Time-kill curves were also determined at concentrations equivalent to MIC90% for the respective oils. Cinnamon oil was the most efficient, with MIC90% values of 0.047 and 0.09 against S. aureus and E. coli, respectively, whereas ginger (0.09), cloves (0.095) and lemon grass (0.1) showed similar activities against S. aureus. Ginger (0.52) and lemon grass (0.55) oils were equivalent in efficiency against E. coli strains. According to the time-kill curves, the obtained MIC90% values could indicate either bactericidal or bacteriostatic effects depending on the tested bacterium. Thus, the studied essential oils were effective to control bacterial development, the antimicrobial potential differed with the tested bacterial species, and Gram-positive bacteria (S. aureus) strains were more susceptible to the tested oils than Gram-negative ones (E. coli).
medicinal plants; essential oils; Staphylococcus aureus; Escherichia coli; antibacterial activity
