Bioactivity of essential oils towards fungi and bacteria: mode of action and mathematical tools

This chapter focuses on the mode of action of essential oils (EOs) towards bacteria and fungi and on the mathematical tools to determine this effect. It offers an overview on the antibacterial activity of EOs with a focus on the most important effects at cell level. The antifungal effect of EOs was the result of hydrogen bonds between the hydroxyl groups of phenolic compounds and the active sites of cellular enzymes. The antimicrobial effect of EOs, as well as of other chemicals or by physical approaches, can be evaluated by using a modified micro‐dilution or by evaluating the growth/inactivation through plating. The approaches can be different for bacteria/yeasts and filamentous fungi; the chapter further focuses on the most important tools, and deals with the evaluation of the combined use of two EOs/compounds. The bioactivity of EOs towards bacteria and yeasts can be evaluated in the same way.