Infectious diseases remain one of the leading causes of morbidity and mortality worldwide. The WHO and CDC have expressed serious concern regarding the continued increase in the development of multidrug resistance among bacteria. Therefore, the antibiotic resistance crisis is one of the most pressing issues in global public health. Associated with the rise in antibiotic resistance is the lack of new antimicrobials. This has triggered initiatives worldwide to develop novel and more effective antimicrobial compounds as well as to develop novel delivery and targeting strategies. Bacteria have developed many ways by which they become resistant to antimicrobials. Among those are enzyme inactivation, decreased cell permeability, target protection, target overproduction, altered target site/enzyme, increased efflux due to over-expression of efflux pumps, among others. Other more complex phenotypes, such as biofilm formation and quorum sensing do not appear as a result of the exposure of bacteria to antibiotics although, it is known that biofilm formation can be induced by antibiotics. These phenotypes are related to tolerance to antibiotics in bacteria. Different strategies, such as the use of nanostructured materials, are being developed to overcome these and other types of resistance. Nanostructured materials can be used to convey antimicrobials, to assist in the delivery of novel drugs or ultimately, possess antimicrobial activity by themselves. Additionally, nanoparticles (e.g., metallic, organic, carbon nanotubes, etc.) may circumvent drug resistance mechanisms in bacteria and, associated with their antimicrobial potential, inhibit biofilm formation or other important processes. Other strategies, including the combined use of plant-based antimicrobials and nanoparticles to overcome toxicity issues, are also being investigated. Coupling nanoparticles and natural-based antimicrobials (or other repurposed compounds) to inhibit the activity of bacterial efflux pumps; formation of biofilms; interference of quorum sensing; and possibly plasmid curing, are just some of the strategies to combat multidrug resistant bacteria. However, the use of nanoparticles still presents a challenge to therapy and much more research is needed in order to overcome this. In this review, we will summarize the current research on nanoparticles and other nanomaterials and how these are or can be applied in the future to fight multidrug resistant bacteria.

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Nano-Strategies to Fight Multidrug Resistant Bacteria-"A Battle of the Titans".

Recent developments in antibacterial and antifungal chitosan and its derivatives.

Wound healing and antimicrobial effect of active secondary metabolites in chitosan-based wound dressings: A review

The worldwide escalation of bacterial resistance to conventional medical antibiotics is a serious concern for modern medicine. High prevalence of multidrug-resistant bacteria among bacteria-based infections decreases effectiveness of current treatments and causes thousands of deaths. New improvements in present methods and novel strategies are urgently needed to cope with this problem. Owing to their antibacterial activities, metallic nanoparticles represent an effective solution for overcoming bacterial resistance. However, metallic nanoparticles are toxic, which causes restrictions in their use. Recent studies have shown that combining nanoparticles with antibiotics not only reduces the toxicity of both agents towards human cells by decreasing the requirement for high dosages but also enhances their bactericidal properties. Combining antibiotics with nanoparticles also restores their ability to destroy bacteria that have acquired resistance to them. Furthermore, nanoparticles tagged with antibiotics hav...

Coping with antibiotic resistance: combining nanoparticles with antibiotics and other antimicrobial agents.

Carvacrol is a monoterpenic phenol produced by an abundant number of aromatic plants, including thyme and oregano. Presently, carvacrol is used in low concentrations as a food flavoring ingredient and preservative, as well as a fragrance ingredient in cosmetic formulations. In recent years, considerable research has been undertaken in an effort to establish the biological actions of carvacrol for its potential use in clinical applications. Results from in vitro and in vivo studies show that carvacrol possess a variety of biological and pharmacological properties including antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory, hepatoprotective, spasmolytic, and vasorelaxant. The focus of this review is to evaluate the existing knowledge regarding the biological, pharmacological, and toxicological effects of carvacrol.

The Bioactivity and Toxicological Actions of Carvacrol

Essential oils are known to possess antimicrobial and antioxidant activity while chitosan is a biocompatible polymer with antibacterial activity against a broad spectrum of bacteria. In this work, nanoparticles with both antioxidant and antibacterial properties were prepared by grafting eugenol and carvacrol (two components of essential oils) on chitosan nanoparticles. Aldehyde groups were first introduced in eugenol and carvacrol, and the grafting of these oils to chitosan nanoparticles was carried out via the Schiff base reaction. The surface concentration of the grafted essential oil components was determined by X-ray photoelectron spectroscopy (XPS). The antioxidant activities of the carvacrol-grafted chitosan nanoparticles (CHCA NPs) and the eugenol-grafted chitosan nanoparticles (CHEU NPs) were assayed with diphenylpicrylhydrazyl (DPPH). Antibacterial assays were carried out with a representative gram-negative bacterium, Escherichia coli (E. coli) and a gram-positive bacterium, Staphylococcus aureus (S. aureus). The grafted eugenol and carvacrol conferred antioxidant activity to the chitosan nanoparticles, and the essential oil component-grafted chitosan nanoparticles achieved an antibacterial activity equivalent to or better than that of the unmodified chitosan nanoparticles. Cytotoxicity assays using 3T3 mouse fibroblast showed that the cytotoxicity of CHEU NPs and CHCA NPs were significant lower than those of the pure essential oils.

Antioxidant and antibacterial activities of eugenol and carvacrol-grafted chitosan nanoparticles.

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Antioxidant and antibacterial activities of eugenol and carvacrol-grafted chitosan nanoparticles.