Standardization of in-vitro methods for determination of antimicrobial properties of essential oils

Abstract

Essential oils (EOs) have been recognized as well tolerated substances with great commercial value that finds applications in traditional medicine. This study systematically reviews various methods published from 2016 to 2020 that were employed to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of essential oils. The main question was, ‘What are the most reliable in-vitro methods to determine MIC and MBC of EOs’? The reported outputs of the search terms for the colony-forming unit (CFU), MIC, MBC, and the zone of inhibition (ZOI) were used to assess the methods.121 studies reported ‘Antibacterial’, 90 ‘Antifungal’, 110 ‘Antimicrobial’, 71 ‘ZOI’, 17 ‘CFU’, and 35 ‘MIC and MBC’. Forty-seven studies were selected according to the criteria for analysis in this review. This review indicated that each study requires its appropriate method. The antimicrobial efficacy of herbal extracts or EOs was not comparable to those of the antibiotics. The use of standard microbial strains is essential when clinical strains are included in the research. Based on the contents and analysis of the published articles, it is clear that designing antimicrobial experiments using EOs would produce more reliable results than those of the extracts. Based on the literature review and our experience, we suggest parameters to consider while determining antimicrobial properties of essential oils.