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      Antibacterial effect of essential oils and their components against Xanthomonas arboricola pv. pruni revealed by microdilution and direct bioautographic assays


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          Bacterial spot of stone fruits caused by Xanthomonas arboricola pv. pruni ( Xap) is one of the most significant diseases of several Prunus species. Disease outbreaks can result in severe economic losses while the control options are limited. Antibacterial efficacy of essential oils (EOs) of thyme, cinnamon, clove, rosemary, tea tree, eucalyptus, lemon grass, citronella grass, and lemon balm was assessed against two Hungarian Xap isolates. The minimal inhibitory concentration (MIC) was determined by broth microdilution assay and for the identification of active EOs’ components a newly introduced high-performance thin-layer chromatography (HPTLC)- Xap (direct bioautography) method combined with solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) was applied. All EOs inhibited both bacterium isolates, but cinnamon proved to be the most effective EO with MIC values of 31.25 µg/mL and 62.5 µg/mL, respectively. Compounds in the antibacterial HPTLC zones were identified as thymol in thyme, trans-cinnamaldehyde in cinnamon, eugenol in clove, borneol in rosemary, terpinen-4-ol in tea tree, citral (neral and geranial) in lemon grass and lemon balm, and citronellal and nerol in citronella grass. Regarding active compounds, thymol had the highest efficiency with a MIC value of 50 µg/mL. Antibacterial effects of EOs have already been proven for several Xanthomonas species, but to our knowledge, the studied EOs, except for lemon grass and eucalyptus, were tested for the first time against Xap. Furthermore, in case of Xap, this is the first report demonstrating that direct bioautography is a fast and suitable method for screening anti- Xap components of complex matrices, like EOs.

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          Essential oils: their antibacterial properties and potential applications in foods--a review.

          In vitro studies have demonstrated antibacterial activity of essential oils (EOs) against Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7, Shigella dysenteria, Bacillus cereus and Staphylococcus aureus at levels between 0.2 and 10 microl ml(-1). Gram-negative organisms are slightly less susceptible than gram-positive bacteria. A number of EO components has been identified as effective antibacterials, e.g. carvacrol, thymol, eugenol, perillaldehyde, cinnamaldehyde and cinnamic acid, having minimum inhibitory concentrations (MICs) of 0.05-5 microl ml(-1) in vitro. A higher concentration is needed to achieve the same effect in foods. Studies with fresh meat, meat products, fish, milk, dairy products, vegetables, fruit and cooked rice have shown that the concentration needed to achieve a significant antibacterial effect is around 0.5-20 microl g(-1) in foods and about 0.1-10 microl ml(-1) in solutions for washing fruit and vegetables. EOs comprise a large number of components and it is likely that their mode of action involves several targets in the bacterial cell. The hydrophobicity of EOs enables them to partition in the lipids of the cell membrane and mitochondria, rendering them permeable and leading to leakage of cell contents. Physical conditions that improve the action of EOs are low pH, low temperature and low oxygen levels. Synergism has been observed between carvacrol and its precursor p-cymene and between cinnamaldehyde and eugenol. Synergy between EO components and mild preservation methods has also been observed. Some EO components are legally registered flavourings in the EU and the USA. Undesirable organoleptic effects can be limited by careful selection of EOs according to the type of food.
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            Essential Oils in Food Preservation: Mode of Action, Synergies, and Interactions with Food Matrix Components

            Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds’ mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.
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              Reclassification of Xanthomonas


                Author and article information

                URI : https://loop.frontiersin.org/people/2256257
                URI : https://loop.frontiersin.org/people/832745
                URI : https://loop.frontiersin.org/people/2184540
                Front Cell Infect Microbiol
                Front Cell Infect Microbiol
                Front. Cell. Infect. Microbiol.
                Frontiers in Cellular and Infection Microbiology
                Frontiers Media S.A.
                14 June 2023
                : 13
                : 1204027
                [1] 1 Plant Protection Institute, Centre for Agricultural Research, Eötvös Lóránd Research Network , Budapest, Hungary
                [2] 2 Department of Pharmacognosy, Faculty of Pharmaceutical Sciences, Semmelweis University , Budapest, Hungary
                [3] 3 Plant Health Bacteriological Diagnostic National Reference Laboratory, Food Chain Safety Laboratory Directorate, National Food Chain Safety Office , Pécs, Hungary
                Author notes

                Edited by: Yangyang Zhao, Jiangsu Academy of Agricultural Sciences (JAAS), China

                Reviewed by: Yiannis Kourkoutas, Democritus University of Thrace, Greece; Shuishan Song, Hebei Academy of Sciences, China

                *Correspondence: Ildikó Schwarczinger, schwarczinger.ildiko@ 123456atk.hu ; Ágnes M. Móricz, moricz.agnes@ 123456atk.hu
                Copyright © 2023 Kolozsváriné Nagy, Móricz, Böszörményi, Ambrus and Schwarczinger

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                : 11 April 2023
                : 01 June 2023
                Page count
                Figures: 2, Tables: 1, Equations: 0, References: 92, Pages: 9, Words: 4481
                Funded by: National Research, Development and Innovation Office , doi 10.13039/501100018818;
                This work was partially supported by the National Research, Development and Innovation Office of Hungary (NKFIH SNN139496).
                Cellular and Infection Microbiology
                Brief Research Report
                Custom metadata
                Molecular Bacterial Pathogenesis

                Infectious disease & Microbiology
                xanthomonas arboricola pv. pruni ,essential oil,high-performance thin-layer chromatography,spme-gc/ms,direct bioautography,broth microdilution assay,antibacterial efficacy


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