Studies on the effects of microwaves on the growth of microbial cultures were searched for in biomedical journals indexed in MEDLINE from 1966 to 2012. The published studies showed that microwaves produce significant effects on the growth of microbial cultures, which vary from the killing of microorganisms to enhancement of their growth. The nature and extent of the effect depend on the frequency of microwaves and the total energy absorbed by the microorganisms. Low energy, low frequency microwaves enhance the growth of microorganisms, whereas high energy, high frequency microwaves destroy the microorganisms. However, neither the effects of a wide spectrum of frequencies nor the effects of a wide range of absorbed energies have been investigated.

The aim of this study was to evaluate and compare the antimicrobial activity of four essential oils that belong to Lamiaceae family (sage, oregano, thyme) and eucalyptus oil. Gas chromatography coupled with mass spectrometry (GC-MS) revealed that the highest percent of essential oils 98.93% include three classes of compounds - monoterpene hydrocarbons, aromatic hydrocarbons and oxidized monoterpenes. The main components are oxidized monoterpenes: carvacrol (59.03%); thymol (36.12%), eucalyptol (20.66%), hydrocarbon monoterpenes: limonene (30.96%) and α-pinene (12.21%) and aromatic monoterpene, p-cymene (22.25%) All essential oils showed great potential of antimicrobial activity against several bacteria and yeast C. albicans, using the agar diffusion method with wells. Minimum inhibitory concentration (MIC) for the essential oils has been determined by the broth dilution method and valued in the range from 1 to 5 μL/m, depending on the essential oil and bacteria tested, and up to 100 μL/ml for C. albicans. The essential oils of Lamiaceae family exhibited a strong antibacterial activity for tested microorganisms, while the essential oils of thyme were especially recognized.