The antimicrobial activity of essential oil compoundsagainst escherichia coli and staphylococcus aureus

Essential oils (EOs) are aromatic and volatile liquids with antimicrobial properties.EOs or their compounds have been shown antibacterial, antiparasitic, insecticidal,antiviral, antifungal, anticancer and antioxidant activities. In the food industry, theyplay an important role in food preservation as effective alternatives or complementsto synthetic preservatives which have a negative consumer perception. However,new applications require more knowledge about the solubility and the minimuminhibitory concentration (MIC) of EOs and their compounds, the effect of theindividual compounds on target microorganisms as well as synergistic/antagonisticinteractions between compounds. In order to fill this knowledge gap, this thesisfocused on seventeen pure compounds of essential oil (EO): ocimene, geraniol,citral, geranyl asetat, menthol, menthone, menthyl asetat, p-cymene, thymol,eugenol, estragole (4-allylanisole), cinnamyl alkol, cinnamaldehyde, α-pinene,camphor, eucalyptol (1,8-cineole) and borneol. More specifically, maximumsoluble concentrations of pure EO compounds supplemented with surfactant and/orsolvent in a water based broth was first tested. Furthermore, their antimicrobialactivity was investigated in vitro using a growth inhibition assay againstEscherichia coli (3 strains), as model organism for the Gram (-) bacteria and againstStaphylococcus aureus (3 strains) as model organism for the Gram (+) bacteria.Some of these compounds such as geraniol (11,25 mM), citral (13,5 mM) andcinnamaldehyde (14,4 mM) expressed antibacterial activity against all tested strainsof S. aureus and E. coli when they are applied as single compounds. Geraniol wasa more effective EO compound against S. aureus than E. coli. The combination ofcinnamaldehyde and p-cymene did not show antagonistic effect towards all testedbacteria. The interaction between cinnamaldehyde and eugenol could be an additiveor synergistic effect against S. aureus LMG8224, which was the most susceptiblebacterium to this combination, and E. coli JG33. The interaction of the samecombination against other tested strains of E. coli and S. aureus was nonantagonism.