Antibacterial and antifungal activity of aromatic constituents of essential oils.Five aromatic constituents of essential oils (cineole, citral, geraniol, linalool and menthol) were tested for antimicrobial activity against eighteen bacteria (including Gram-positive cocci and rods, and Gram-negative rods) and twelve fungi (three yeast-like and nine filamentous). In terms of antibacterial activity linalool was the most effective and inhibited seventeen bacteria, followed by cineole, geraniol (each of which inhibited sixteen bacteria), menthol and citral aromatic compounds, which inhibited fifteen and fourteen bacteria, respectively. Against fungi the citral and geraniol oils were the most effective (inhibiting all twelve fungi), followed by linalool (inhibiting ten fungi), cineole and menthol (each of which inhibited seven fungi) compounds.
Antibacterial and antifungal activity of ten essential oils in vitro.The essential oils of aegle, ageratum, citronella, eucalyptus, geranium, lemongrass, orange, palmarosa, patchouli and peppermint, were tested for antibacterial activity against 22 bacteria, including Gram-positive cocci and rods and Gram-negative rods, and twelve fungi (3 yeast-like and 9 filamentous) by the disc diffusion method. Lemongrass, eucalyptus, peppermint and orange oils were effective against all the 22 bacterial strains. Aegle and palmarosa oils inhibited 21 bacteria; patchouli and ageratum oils inhibited 20 bacteria and citronella and geranium oils were inhibitory to 15 and 12 bacterial strains, respectively. All twelve fungi were inhibited by seven oils (aegle, citronella, geranium, lemongrass, orange, palmarosa and patchouli). Eucalyptus and peppermint oils were effective against eleven fungi. Ageratum oil was inhibitory to only four fungi tested. The MIC of eucalyptus, lemongrass, palmarosa and peppermint oils ranged from 0.16 to > 20 microliters ml-1 for eighteen bacteria and from 0.25 to 10 microliters ml-1 for twelve fungi.
Effect of essential oils on the viability and morphology of Escherichia coli (SP-11).The four essential oils (aromatic plant products) from palmarosa (Pm), lemongrass (Lg), peppermint (Pt) and eucalyptus (Eu) plants were found to be bactericidal to Escherichia coli strain SP-11, at a concentration of 1.66 (Pm, Lg and Eu) or 2.5 (Pt) microl ml-1. This effect was observed both at 37 degrees C and 4 degrees C and was not prevented by immediate tenfold dilution or by the presence of 0.5 M sucrose. Pm and Pt but not Lg or Eu induced the formation of elongated filamentous forms, some measuring 60-70 micrometers long.