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The aim of this study was to identify antimicrobial properties of selected essential oils in the vapour phase against different strains of Staphylococcus aureus, including MRSA and resistant clinical isolates. The resistance pattern of used S. aureus strains was checked by disc diffusion method against three antibiotics. Essential oils tested were obtained by hydro-distillation and characterized by GC-MS and SPME-GC. Their antimicrobial properties in the vapour phase were determined by the microatmosphere method. Among the essential oils tested, the most active was Armoracia rusticana with MICs ranging from 8.3 to 17 µl/l, followed by Origanum syriacum (8.3-130 µl/l), Allium sativum (8.3-530 µl/l), Satureja hortensis (17-130 µl/l), Satureja montana (33-260 µl/l), Thymus vulgaris (33-260 µl/l), and Thymus serpyllum (33-530 µl/l). To the best of our knowledge, this is the first report of their antimicrobial properties in vapour phase against a collection of strains and clinical isolates of S. aureus, including MRSA. Based on the results, the essential oils tested can be considered as effective anti-staphylococcal natural products with specific application possibilities due to the activity in the vapour phase.

In this study, we analyzed the chemical composition of volatile oils hydrodistilled from seeds of Consolida regalis, Delphinium elatum, Nigella hispanica, and N. nigellastrum using GC and GC/MS. In C. regalis, octadecenoic (77.79%) and hexadecanoic acid (8.34%) were the main constituents. Similarly, the oils from D. elatum and N. hispanica seeds consisted chiefly of octadecadienoic (42.83 and 35.58%, resp.), hexadecanoic (23.87 and 28.59%, resp.), and octadecenoic acid (21.67 and 19.76%, resp.). Contrastingly, the monoterpene hydrocarbons α-pinene (34.67%) and β-pinene (36.42%) were the main components of N. nigellastrum essential oil. Our results confirm the presence of essential oils in the family Ranunculaceae and suggest chemotaxonomical relationships within the representatives of the genera Consolida, Delphinium, and Nigella. In addition, the presence of various bioactive constituents such as linoleic acid, (-)-β-pinene, squalene, or carotol in seeds of D. elatum, N. hispanica, and N. nigellastrum indicates a possible industrial use of these plants.

The vapor phase of some essential oils proved to have antimicrobial activity. Utilization of the vapor phase of Eos is presently understood as one of the possible alternatives to synthetic food preservatives which could be used in the future. However, testing the vapor phase of EOs against microorganisms causing food-borne diseases (e.g. Salmonella enteritidis or Staphylococcus aureus) or food spoilage is relatively new. Consequently, due to the large number of known EOs, research on their antimicrobial activity is still largely in the phase of in vitro rather than in vivo testing. Moreover, no standard and reliable method for fast screening of a wide range of samples exists. Thus, the aim of this study is to show results concerning tests of the antimicrobial activity of EOs against S. enteritidis or S. aureus, which were conducted by two modifications of the disc volatilization method we developed. The lately developed method has the potential to become widely used for fast screening of EO antimicrobial activity in the vapor phase.

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