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This work evaluates the in vitro inhibitory activity of 70 essential oils (EOs) in the vapor phase for the control of Chalkbrood disease caused by Ascosphaera apis Maassen ex Claussen (Olive et Spiltoir). Two wild strains isolated from infected honey bee colonies together with one standard collection strain were tested by the microatmosphere method. From 70 EOs, 39 exhibited an antifungal effect against A. apis standard and wild strains. The greatest antifungal action was observed for EO vapors from Armoracia rusticana, followed by Thymus vulgaris, Cymbopogon flexosus, Origanum vulgare and Allium sativum. An investigation of chemical composition by GC-MS revealed, that the most active EOs contained allyl isothiocyanate, citral, carvacrol and diallyl sulfides as the main constituents. The chemical composition plays a key role, as activities of different EOs from the same botanical species were different according to their composition.

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.