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      Activity of Specialized Biomolecules against Gram-Positive and Gram-Negative Bacteria

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          Abstract

          The increased resistance of bacteria against conventional pharmaceutical solutions, the antibiotics, has raised serious health concerns. This has stimulated interest in the development of bio-based therapeutics with limited resistance, namely, essential oils (EOs) or antimicrobial peptides (AMPs). This study envisaged the evaluation of the antimicrobial efficacy of selected biomolecules, namely LL37, pexiganan, tea tree oil (TTO), cinnamon leaf oil (CLO) and niaouli oil (NO), against four bacteria commonly associated to nosocomial infections: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. The antibiotic vancomycin and silver nanoparticles (AgNPs) were used as control compounds for comparison purposes. The biomolecules were initially screened for their antibacterial efficacy using the agar-diffusion test, followed by the determination of minimal inhibitory concentrations (MICs), kill-time kinetics and the evaluation of the cell morphology upon 24 h exposure. All agents were effective against the selected bacteria. Interestingly, the AgNPs required a higher concentration (4000–1250 μg/mL) to induce the same effects as the AMPs (500–7.8 μg/mL) or EOs (365.2–19.7 μg/mL). Pexiganan and CLO were the most effective biomolecules, requiring lower concentrations to kill both Gram-positive and Gram-negative bacteria (62.5–7.8 μg/mL and 39.3–19.7 μg/mL, respectively), within a short period of time (averaging 2 h 15 min for all bacteria). Most biomolecules apparently disrupted the bacteria membrane stability due to the observed cell morphology deformation and by effecting on the intracellular space. AMPs were observed to induce morphological deformations and cellular content release, while EOs were seen to split and completely envelope bacteria. Data unraveled more of the potential of these new biomolecules as replacements for the conventional antibiotics and allowed us to take a step forward in the understanding of their mechanisms of action against infection-related bacteria.

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          Metal nanoparticles: understanding the mechanisms behind antibacterial activity

          As the field of nanomedicine emerges, there is a lag in research surrounding the topic of nanoparticle (NP) toxicity, particularly concerned with mechanisms of action. The continuous emergence of bacterial resistance has challenged the research community to develop novel antibiotic agents. Metal NPs are among the most promising of these because show strong antibacterial activity. This review summarizes and discusses proposed mechanisms of antibacterial action of different metal NPs. These mechanisms of bacterial killing include the production of reactive oxygen species, cation release, biomolecule damages, ATP depletion, and membrane interaction. Finally, a comprehensive analysis of the effects of NPs on the regulation of genes and proteins (transcriptomic and proteomic) profiles is discussed.
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            Characterization of enhanced antibacterial effects of novel silver nanoparticles

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              Antibacterial and antifungal properties of essential oils.

              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.
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                Author and article information

                Journal
                Antibiotics (Basel)
                Antibiotics (Basel)
                antibiotics
                Antibiotics
                MDPI
                2079-6382
                09 June 2020
                June 2020
                : 9
                : 6
                : 314
                Affiliations
                Centre for Textile Science and Technology (2C2T), Department of Textile Engineering, University of Minho, Campus of Azurém, 4800-058 Guimarães, Portugal; taniatav@ 1234562c2t.uminho.pt (T.D.T.); joana.antunes@ 1234562c2t.uminho.pt (J.C.A.); padraoj@ 1234562c2t.uminho.pt (J.P.); afr@ 1234562c2t.uminho.pt (A.I.R.); azille@ 1234562c2t.uminho.pt (A.Z.); mtamorim@ 123456det.uminho.pt (M.T.P.A.); fnunes@ 123456det.uminho.pt (F.F.)
                Author notes
                [* ]Correspondence: helena.felgueiras@ 1234562c2t.uminho.pt ; Tel.: +351-253-510-283; Fax: +351-253-510-293
                Author information
                https://orcid.org/0000-0003-2994-6767
                https://orcid.org/0000-0003-2036-2730
                https://orcid.org/0000-0001-5630-6621
                https://orcid.org/0000-0001-9556-6311
                https://orcid.org/0000-0001-5299-4164
                https://orcid.org/0000-0002-4354-0256
                Article
                antibiotics-09-00314
                10.3390/antibiotics9060314
                7344598
                32526972
                acbc7b89-2695-4070-ab74-6c4b23b60e20
                © 2020 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
                : 11 May 2020
                : 08 June 2020
                Categories
                Article

                antimicrobial peptides,essential oils,minimum inhibitory concentration,bactericidal,nosocomial

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