Extensive documentation on the antimicrobial properties of essential oils and their constituents has been carried out by several workers. Although the mechanism of action of a few essential oil components has been elucidated in many pioneering works in the past, detailed knowledge of most of the compounds and their mechanism of action is still lacking. This knowledge is particularly important for the determination of the effect of essential oils on different microorganisms, how they work in combination with other antimicrobial compounds, and their interaction with food matrix components. Also, recent studies have demonstrated that nanoparticles (NPs) functionalized with essential oils have significant antimicrobial potential against multidrug- resistant pathogens due to an increase in chemical stability and solubility, decreased rapid evaporation and minimized degradation of active essential oil components. The application of encapsulated essential oils also supports their controlled and sustained release, which enhances their bioavailability and efficacy against multidrug-resistant pathogens. In the recent years, due to increasingly negative consumer perceptions of synthetic preservatives, interest in essential oils and their application in food preservation has been amplified. Moreover, the development of resistance to different antimicrobial agents by bacteria, fungi, viruses, parasites, etc. is a great challenge to the medical field for treating the infections caused by them, and hence, there is a pressing need to look for new and novel antimicrobials. To overcome these problems, nano-encapsulation of essential oils and exploiting the synergies between essential oils, constituents of essential oils, and antibiotics along with essential oils have been recommended as an answer to this problem. However, less is known about the interactions that lead to additive, synergistic, or antagonistic effects. A contributing role of this knowledge could be the design of new and more potent antimicrobial blends, and understanding of the interplay between the components of crude essential oils. This review is written with the purpose of giving an overview of current knowledge about the antimicrobial properties of essential oils and their mechanisms of action, components of essential oils, nano-encapsulated essential oils, and synergistic combinations of essential oils so as to find research areas that can facilitate applications of essential oils to overcome the problem of multidrug-resistant micro-organisms.

Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives.

Metal‐Based Nanomaterials in Biomedical Applications: Antimicrobial Activity and Cytotoxicity Aspects

https://dspace.stir.ac.uk/bitstream/1893/27786/1/1-s2.0-S000186861630392X-main.pdf

Formulation, stabilisation and encapsulation of bacteriophage for phage therapy

Introduction Silver nanoparticles (AgNPs) are of great interest due to their unique and controllable characteristics. Different synthesis methods have been proposed to produce these nanoparticles, which often require elevated temperatures/pressures or toxic solvents. Thus, green synthesis could be a replacement option as a simple, economically viable and environmentally friendly alternative approach for the synthesis of silver nanoparticles. Methods Here, the potential of the walnut green husk was investigated in the production of silver nanoparticles. An aqueous solution extracted from walnut green husk was used as a reducing agent as well as a stabilizing agent. Then, the synthesized nanoparticles were characterized with respect of their anticancer, antioxidant, and antimicrobial properties. Results Results showed that the synthesized nanoparticles possessed an average size of 31.4 nm with a Zeta potential of -33.8 mV, indicating high stability. A significant improvement in the cytotoxicity and antioxidant characteristics of the green synthesized Ag nanoparticles against a cancerous cell line was observed in comparison with the walnut green husk extract and a commercial silver nanoparticle (CSN). This could be due to a synergistic effect of the synthesized silver nanoparticles and their biological coating. AgNPs and the extract exhibited 70% and 40% cytotoxicity against MCF-7 cancerous cells, respectively, while CSN caused 56% cell death (at the concentration of 60 µg/mL). It was observed that AgNPs were much less cytotoxic when tested against a noncancerous cell line (L-929) in comparison with the control material (CSN). The free radical scavenging analysis demonstrated profound anti-oxidant activity for the synthesized nanoparticles in comparison with the extract and CSN. It was also detected that the synthesized AgNPs possess antibacterial activity against nosocomial and standard strains of both Gram-positive and Gram-negative bacteria (minimum inhibitory concentration =5-30 µg/mL). Conclusion These findings imply that the synthesized nanoparticles using green nanotechnology could be an ideal strategy to combat cancer and infectious diseases.

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Selective cytotoxicity of green synthesized silver nanoparticles against the MCF-7 tumor cell line and their enhanced antioxidant and antimicrobial properties

Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant Gram-negative and Gram-positive bacteria1. Tigecycline resistance has sporadically occurred in recent years, primarily due to chromosome-encoding mechanisms, such as overexpression of efflux pumps and ribosome protection2,3. Here, we report the emergence of the plasmid-mediated mobile tigecycline resistance mechanism Tet(X4) in Escherichia coli isolates from China, which is capable of degrading all tetracyclines, including tigecycline and the US FDA newly approved eravacycline. The tet(X4)-harbouring IncQ1 plasmid is highly transferable, and can be successfully mobilized and stabilized in recipient clinical and laboratory strains of Enterobacteriaceae bacteria. It is noteworthy that tet(X4)-positive E. coli strains, including isolates co-harbouring mcr-1, have been widely detected in pigs, chickens, soil and dust samples in China. In vivo murine models demonstrated that the presence of Tet(X4) led to tigecycline treatment failure. Consequently, the emergence of plasmid-mediated Tet(X4) challenges the clinical efficacy of the entire family of tetracycline antibiotics. Importantly, our study raises concern that the plasmid-mediated tigecycline resistance may further spread into various ecological niches and into clinical high-risk pathogens. Collective efforts are in urgent need to preserve the potency of these essential antibiotics. Plasmid-encoded tet(X) genes from Escherichia coli in China confer high-level tigecycline resistance.

Plasmid-encoded tet(X) genes that confer high-level tigecycline resistance in Escherichia coli.

Methods for in vitro evaluating antimicrobial activity: A review

Reduction of biofilm formation on 3D printing materials treated with essential oils major compounds

Effect of preconditioning cobalt and nickel based dental alloys with Bacillus sp. extract on their surface physicochemical properties and theoretical prediction of Candida albicans adhesion.

In this study, we investigated firstly the evolution of physicochemical properties before and after the spores adhesion of Penicillium expansum and Penicillium commun on the surface of cedar wood. Secondly, we also observed the variation of the physicochemical properties after the dual adhesion of these two fungal strains. Thus, we found that the cedar was initially hydrophobic (θw =118.5° ΔGiwi = -6.09 mJ/m 2 ) with a significantly higher electron donor character (γ - = 31.15 mJ/m 2 ) than the electron acceptor (γ + = 8.75 mJ/m 2 ). Then these surface properties of cedar were significantly changed following the adhesion of spores according to the contact time and depending on the Penicillium strains. The values for the physicochemical characteristics were (θw = 87.8°; ΔGiwi = -93.46 mJ/m 2 γ - = 0.06 mJ/m 2 and γ + = 0.57 mJ/m 2 ) after 24 hours of incubation with the spores of P. expansum and (θw = 96 °; ΔGiwi = -46.18 mJ/m 2 ; γ - = 4.09 mJ/m 2 and γ + = 4.40 mJ/m 2 ) with those of P. commun. However, although hydrophobicity is still maintained after the combined spore adhesion (P. commun + P. expansum), the latter allowed to find a significant increase of Lewis acid/base parameters compared to the single spore adhesions.

Comparison of the evolution of physico-chemical properties due to the single and combined adhesion of two species of the Penicillium genus on cedar wood.

A new composition silver doped-bioglass: Synthesis, in vitro bioactivity and antibacterial study and comparison with the binary SiO2-CaO and ternary SiO2-CaO-P2O5 systems

Moulay Sadiki

Papers

Methods for in vitro evaluating antimicrobial activity: A review

Reduction of biofilm formation on 3D printing materials treated with essential oils major compounds

Effect of preconditioning cobalt and nickel based dental alloys with Bacillus sp. extract on their surface physicochemical properties and theoretical prediction of Candida albicans adhesion.

Comparison of the evolution of physico-chemical properties due to the single and combined adhesion of two species of the Penicillium genus on cedar wood.

A new composition silver doped-bioglass: Synthesis, in vitro bioactivity and antibacterial study and comparison with the binary SiO2-CaO and ternary SiO2-CaO-P2O5 systems