In recent years there has been an increasing interest in the use of natural substances, and some questions concerning the safety of synthetic compounds have encouraged more detailed studies of plant resources. Essential oils, odorous and volatile products of plant secondary metabolism, have a wide application in folk medicine, food flavouring and preservation as well as in fragrance industries. The antimicrobial properties of essential oils have been known for many centuries. In recent years (1987-2001), a large number of essential oils and their constituents have been investigated for their antimicrobial properties against some bacteria and fungi in more than 500 reports. This paper reviews the classical methods commonly used for the evaluation of essential oils antibacterial and antifungal activities. The agar diffusion method (paper disc and well) and the dilution method (agar and liquid broth) as well as turbidimetric and impedimetric monitoring of microorganism growth in the presence of tested essential oils are described. Factors influencing the in vitro antimicrobial activity of essential oils and the mechanisms of essential oils action on microorganisms are reported. This paper gives an overview on the susceptibility of human and food-borne bacteria and fungi towards different essential oils and their constituents. Essential oils of spices and herbs (thyme, origanum, mint, cinnamon, salvia and clove) were found to possess the strongest antimicrobial properties among many tested.

This review article discusses the active constituents and potential of two menthol mint oils, Mentha piperita (MPEO) and Mentha arvensis (MAEO), as natural sources for botanical pesticides. The biological activities of these menthol mint oils, which can be useful in agriculture, have been broadly researched, especially toward phytotoxic microorganisms. To a lesser extent, the insecticidal and herbicidal activities of mint EOs have also been studied. It is apparent that the prospect of using menthol mint oils in agriculture is increasing in popularity. A number of investigations showed that the in vitro efficacy of MPEO and MAEO, as well as that of their main constituent, menthol, is pronounced. The results of in vitro research are useful for choosing EOs for further investigations. However, it is clear that in situ experiments are crucial and should be more extensively developed. At the same time, known techniques are to be applied to this area and new methods should be worked out, aiming at the improvement of EOs’ pesticidal efficacy and cost-effectiveness, for future implementation in agricultural pest control.

Essential oils obtained from the NR (normal roots) and HR (hairy roots) of the medicinal plant Leonurus sibiricus root were used in this study. The essential oil compositions were detected by GC‐MS. Eighty‐five components were identified in total. Seventy components were identified for NR essential oil. The major constituents in NR essential oil were β‐selinene (9.9%), selina‐4,7‐diene (9.7%), (E)‐β‐caryophyllene (7.3%),myli‐4(15)‐ene (6.4%), and guaia‐1(10),11‐diene (5.9%). Sixty‐seven components were identified in HR essential oil, the main constituents being (E)‐β‐caryophyllene (22.6%), and germacrene D (19.8%). The essential oils were tested for cytotoxic effect, antimicrobial, anti‐inflammatory, and antioxidant activities. Both essential oils showed activity against grade IV glioma cell lines (IC₅₀ = 400 μg/mL), antimicrobial (MIC and MFC values of 2500 to 125 μg/mL), and anti‐inflammatory (decreased level of IL‐1β, IL‐6, TNF‐α, and IFN‐γ in LPS‐stimulated cells).The essential oils exhibited moderate antioxidant activity in ABTS (EC₅₀ = 98 and 88 μg/mL) assay. This is the first study to examine composition of the essential oils and their antimicrobial, antioxidant, antiproliferative, and anti‐inflammatory activities. The results indicate that essential oils form L. sibiricus root may be used in future as an alternative to synthetic antimicrobial agents with potential application in the food and pharmaceutical industries.

The essential oils obtained by hydrodistillation of dried aerial parts of Salvia sclarea L. plants, regenerated in vitro and reproduced from seeds, were analyzed by GC and GC-MS. The oils from in vitro and in vivo plants were compared in respect to their chemical composition as well as antimicrobial and cytotoxic activities. The chemical profiles of both oils were very similar, although the yield of essential oil from in vitro plants was lower (0.1%, v/w) than the oil yield isolated from in vivo S. sclarea plants (0.2%, v/w). Both oils showed antimicrobial and cytotoxic activity. The oil from in vitro regenerated plants of S. sclarea exhibited stronger cytotoxic action against NALM-6 cell lines in comparison with the essential oil from in vivo plants.