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      Antimicrobial Activity of Six Essential Oils Against a Group of Human Pathogens: A Comparative Study

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          Abstract

          Essential oils are concentrated natural extracts derived from plants, which were proved to be good sources of bioactive compounds with antioxidative and antimicrobial properties. This study followed the effect of some commonly used essential oils in micellar and aqueous extract on some of the most common pathogenic bacteria. Frankincense, myrtle, thyme, lemon, oregano and lavender essential oils were tested against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Both micellar and aqueous extracts were used for determination of their minimal inhibitory (MIC) and bactericidal concentrations (MBC). The most active oils were oregano, thyme, lemon and lavender, while the least active were frankincense and myrtle. Oregano oil presented up to 64 times lower MICs/MBCs than ethylic alcohol, if considered as standard, on all bacteria. Most susceptible bacteria were the Gram-positive cocci, including methicillin resistant S. aureus, while the most resistant was P. aeruginosa. With some exceptions, the best activity was achieved by micelles suspension of essential oils, with MICs and MBCs ranging from 0.1% to > 50% v/v. Only oregano and lavender aqueous extracts presented bactericidal activity and only on K. pneumoniae (MIC = 6.3%). Thyme, lemon and oregano oils present significantly lower overall average MICs for their micellar form than for their aqueous extracts. The present results may suggest some formulas of colloid or micelle suspensions of whole essential oils such as oregano, thyme or lemon oil, that may help in antimicrobial fight. Aqueous extracts of oregano or thyme oil with good antibacterial activity could also be used in selected cases.

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          Most cited references42

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          Antimicrobial activity of essential oils and other plant extracts.

          The antimicrobial activity of plant oils and extracts has been recognized for many years. However, few investigations have compared large numbers of oils and extracts using methods that are directly comparable. In the present study, 52 plant oils and extracts were investigated for activity against Acinetobacter baumanii, Aeromonas veronii biogroup sobria, Candida albicans, Enterococcus faecalis, Escherichia col, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serotype typhimurium, Serratia marcescens and Staphylococcus aureus, using an agar dilution method. Lemongrass, oregano and bay inhibited all organisms at concentrations of < or = 2.0% (v/v). Six oils did not inhibit any organisms at the highest concentration, which was 2.0% (v/v) oil for apricot kernel, evening primrose, macadamia, pumpkin, sage and sweet almond. Variable activity was recorded for the remaining oils. Twenty of the plant oils and extracts were investigated, using a broth microdilution method, for activity against C. albicans, Staph. aureus and E. coli. The lowest minimum inhibitory concentrations were 0.03% (v/v) thyme oil against C. albicans and E. coli and 0.008% (v/v) vetiver oil against Staph. aureus. These results support the notion that plant essential oils and extracts may have a role as pharmaceuticals and preservatives.
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            The antibacterial mechanism of carvacrol and thymol against Escherichia coli.

            To investigate the antibacterial mechanism of carvacrol and thymol against Escherichia coli. The time-kill curve results showed that carvacrol and thymol at 200 mg l(-1) could inhibit the growth of E. coli. Flow cytometry and fluorescent dyes were used to explore the effect of two components on membrane permeability and membrane potential. In membrane permeability experiment, the mean fluorescence intensity of cells treated with 200 mg l(-1) carvacrol or thymol were lower than nonexposed cells. The ratio of red to green fluorescence intensity of DiOC2(3) reflected the change of membrane potential. Carvacrol and thymol at 200 mg l(-1) caused the ratio of red/green decreasing from 0.42 of control to 0.08 and 0.07, respectively. Carvacrol and thymol had desired antimicrobial effect on E. coli. The antibacterial effects were attributed to their ability to permeabilize and depolarize the cytoplasmic membrane. This study showed the potential use of flow cytometry as a suitable method to investigate the mode of antibacterial action of essential oil components.
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              Essential oils: extraction, bioactivities, and their uses for food preservation.

              Essential oils are concentrated liquids of complex mixtures of volatile compounds and can be extracted from several plant organs. Essential oils are a good source of several bioactive compounds, which possess antioxidative and antimicrobial properties. In addition, some essential oils have been used as medicine. Furthermore, the uses of essential oils have received increasing attention as the natural additives for the shelf-life extension of food products, due to the risk in using synthetic preservatives. Essential oils can be incorporated into packaging, in which they can provide multifunctions termed "active or smart packaging." Those essential oils are able to modify the matrix of packaging materials, thereby rendering the improved properties. This review covers up-to-date literatures on essential oils including sources, chemical composition, extraction methods, bioactivities, and their applications, particularly with the emphasis on preservation and the shelf-life extension of food products.
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                Author and article information

                Journal
                Pathogens
                Pathogens
                pathogens
                Pathogens
                MDPI
                2076-0817
                28 January 2019
                March 2019
                : 8
                : 1
                : 15
                Affiliations
                [1 ]Department of Microbiology, University of Medicine, Pharmacy, Sciences and Technology of Târgu Mureș, Târgu Mureș 540139, Romania; mareanca@ 123456gmail.com
                [2 ]Ionian Dept. (DJSGEM), Microbiology and Virology Lab., University Hospital of Bari, 70124 Bari, Italy
                [3 ]Polypheno srl Academic Spin Off, University of Bari, 70124 Bari, Italy
                [4 ]University of Medicine, Pharmacy, Sciences and Technology of Târgu Mureș, Târgu Mureș 540139, Romania; romeofloris@ 123456gmail.com
                [5 ]Pediatrics Clinic 1, University of Medicine, Pharmacy, Sciences and Technology of Târgu Mureș, Târgu Mureș 540139, Romania; lidia.man@ 123456gmail.com
                Author notes
                Author information
                https://orcid.org/0000-0001-5281-0601
                https://orcid.org/0000-0001-5671-8124
                Article
                pathogens-08-00015
                10.3390/pathogens8010015
                6471180
                30696051
                54adedd9-d49e-46b8-9bc5-98a22fb26327
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 06 January 2019
                : 23 January 2019
                Categories
                Article

                antimicrobial agents,micelles,minimum inhibitory concentration (mic),methicillin-resistant staphylococcus aureus (mrsa),volatile oils

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