In total, eight samples of different sandalwoods [Amyris balsamifera L., Santalum album L. and Santalum spicatum (R.Br.) A.DC.] and a mixture of α α α α α-and β β β β β-santalols, as well as eugenol as reference compound, were tested by an agar dilution and agar diffusion method for their antimicrobial activities against the yeast Candida albicans, the Grampositive bacterium Staphylococcus aureus and the Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. The main compounds of each essential oil were investigated by gas chromatographic-spectroscopic (GC-FID and GC-MS) and -olfactory methods to obtain information about the influence of these volatiles on the observed antimicrobial effects. For the santalol mixture, as well as for one S. album and one S. spicatum sample with moderate concentrations of santalols, antimicrobial activity was found against all the strains used. The A. balsamifera sample, containing only a small quantity of α α α α α-santalol and nearly no β β β β β-santalol, showed high effects only against Klebsiella pneumoniae, while against the other strains weak or no activity was observed. Therefore, santalols in medium and/or high concentrations in sandalwood oils show a significant influence on antimicrobial potential in such natural products.

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The oxygenated monoterpenes 1,8-cineole, α-terpineol, terpinen-4-ol and camphor as well as essential oils of pine, rosemary and tea tree, rich in these volatiles, were tested for their antimicrobial activities against some different strains of yeast, Gram-(-)- and Gram-(+)-bacteria by agar diffusion and agar dilution method, respectively. The same was done using the phenolic aroma compound eugenol as a reference-substance. The monoterpene alcohols a-terpineol and terpinen-4-ol were found to be active against all strains used in a wide range. The same result was obtained for the testings of essential oils of pine, rosemary (2 samples) and tea tree. Nearly all aroma chemicals and essential oils did show a significant high antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa. For qualitative and quantitaive investigations of the key aroma compounds and the compositions of the essential oils, gas chromatographic methods (GC-FID and GCMS with columns of different polarities) were used and the results correlated with that of the antimicrobial testings. The obtained data are discussed to get more insight into the influence of pure aroma compounds on antimicrobial activities of essential oils.

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