Indigenous medicinal plant of Ethiopia has been applied for the first time to investigate the synergistic influence of phytoconstituents in green copper nanoparticles (g-Cu NPs) towards the enhancement of antimicrobial properties of NPs. We report the green synthesis of Cu NPs using Hagenia abyssinica (Brace) JF. Gmel. leaf extract. The synthesized g-Cu NPs were characterized by UV-visible, UV-DRS, FT-IR, XRD, SEM, EDXA, TEM, HRTEM, and SAED techniques. The maximum absorbance, , was found to be 403 nm for g-Cu NPs due to surface plasmon resonance. The energy gap, of NPs, was found to be 2.19 eV. FTIR spectra confirmed the presence of polyphenols, tannins, and glycosides in the leaf extract of Hagenia abyssinica. The spectral band at 740 cm-1 is a characteristic of interaction between Cu and biomolecules of the extract. The XRD analysis revealed that the g-Cu NPs appears to be more crystalline in nature. SEM and TEM micrographs showed a mix of spherical, hexagonal, triangular, cylindrical, and irregularly shaped Cu particles. The average particle size of NPs was found to be 34.76 nm by ImageJ analysis. EDX analysis confirmed the presence of copper in the g-Cu NPs. In addition, the SAED pattern of g-Cu NPs presented concentric circular patterns for 4 major planes of crystalline copper and its oxides. The experimental and calculated - spacing values of one of the crystal planes (111) were found to be 0.2432 nm and 0.2444 nm, respectively. The - spacing values of 0.2444 nm and 0.2040 nm correspond to d111Cu2O and d111Cu lattice fringes, respectively. The antibacterial test conducted on E. coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis showed good zone of inhibitions 12.7, 12.7, 14.7, and 14.2 mm, respectively, proving potentiality of g-Cu NPs as a remedy for infectious diseases caused by tested pathogens.

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Synthesis of Green Copper Nanoparticles Using Medicinal Plant Hagenia abyssinica (Brace) JF. Gmel. Leaf Extract: Antimicrobial Properties

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Perspectives on New Crops and New Uses

The increasing incidence of drug- resistant pathogens raises an urgent need to identify and isolate new bioactive compounds from medicinal plants using standardized modern analytical procedures. Medicinal plant-derived compounds could provide novel straightforward approaches against pathogenic bacteria. This review explores the antimicrobial activity of plant-derived components, their possible mechanisms of action, as well as their chemical potential. The focus is put on the current challenges and future perspectives surrounding medicinal plants antimicrobial activity. There are some inherent challenges regarding medicinal plant extracts and their antimicrobial efficacy. Appropriate and optimized extraction methodology plant species dependent leads to upgraded and selective extracted compounds. Antimicrobial susceptibility tests for the determination of the antimicrobial activity of plant extracts may show variations in obtained results. Moreover, there are several difficulties and problems that need to be overcome for the development of new antimicrobials from plant extracts, while efforts have been made to enhance the antimicrobial activity of chemical compounds. Research on the mechanisms of action, interplay with other substances, and the pharmacokinetic and/or pharmacodynamic profile of the medicinal plant extracts should be given high priority to characterize them as potential antimicrobial agents.

Towards Advances in Medicinal Plant Antimicrobial Activity: A Review Study on Challenges and Future Perspectives.

Due to the increasing prevalence of life-threatening bacterial, fungal and viral infections and the ability of these human pathogens to develop resistance to current treatment strategies, there is a great need to find and develop new compunds to combat them. These molecules must have low toxicity, specific activity and high bioavailability. The most suitable compounds for this task are usually derived from natural sources (animal, plant or even microbial). In this review article, the latest and most promising natural compounds used to combat bacteria, filamentous fungi and viruses are presented and evaluated. These include plant extracts, essential oils, small antimicrobial peptides of animal origin, bacteriocins and various groups of plant compounds (triterpenoids; alkaloids; phenols; flavonoids) with antimicrobial and antiviral activity. Data are presented on the inhibitory activity of each natural antimicrobial substance and on the putative mechanism of action against bacterial and fungal strains. The results show that among the bioactive compounds studied, triterpenoids have significant inhibitory activity against coronaviruses, but flavonoids have also been shown to inhibit SARS-COV-2. The last chapter is devoted to nanocarriers used to improve stability, bioavailability, cellular uptake/internalization, pharmacokinetic profile and reduce toxicity of natural compunds. There are a number of nanocarriers such as liposomes, drug delivery microemulsion systems, nanocapsules, solid lipid nanoparticles, polymeric micelles, dendrimers, etc. However, some of the recent studies have focused on the incorporation of natural substances with antimicrobial/antiviral activity into polymeric nanoparticles, niosomes and silver nanoparticles (which have been shown to have intrinsic antimicrobial activity). The natural antimicrobials isolated from animals and microorganisms have been shown to have good inhibitory effect on a range of pathogens, however the plants remain the most prolific source. Even if the majority of the studies for the biological activity evaluation are in silico or in vitro, their internalization in the optimum nanocarriers represents the future of "green therapeutics" as shown by some of the recent work in the field.

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Natural Compounds With Antimicrobial and Antiviral Effect and Nanocarriers Used for Their Transportation.

Microbial resistance has progressed rapidly and is becoming the leading cause of death globally. The spread of antibiotic-resistant microorganisms has been a significant threat to the successful therapy against microbial infections. Scientists have become more concerned about the possibility of a return to the pre-antibiotic era. Thus, searching for alternatives to fight microorganisms has become a necessity. Some bacteria are naturally resistant to antibiotics, while others acquire resistance mainly by the misuse of antibiotics and the emergence of new resistant variants through mutation. Since ancient times, plants represent the leading source of drugs and alternative medicine for fighting against diseases. Plants are rich sources of valuable secondary metabolites, such as alkaloids, quinones, tannins, terpenoids, flavonoids, and polyphenols. Many studies focus on plant secondary metabolites as a potential source for antibiotic discovery. They have the required structural properties and can act by different mechanisms. This review analyses the antibiotic resistance strategies produced by multidrug-resistant bacteria and explores the phytochemicals from different classes with documented antimicrobial action against resistant bacteria, either alone or in combination with traditional antibiotics.

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Review on the Antibacterial Mechanism of Plant-Derived Compounds against Multidrug-Resistant Bacteria (MDR).

The emergence and spread of antibiotic resistance, as well as the evolution of new strains of disease causing agents, are of great concern to the global health community. Effective treatment of a disease entails the development of new pharmaceuticals or some potential source of novel drugs. Commonly used medicinal plants of our community could be an excellent source of drugs to fight off this problem. This study is focused on exploring the antimicrobial properties of the plants that are commonly being used as traditional medicines. The antimicrobial potential of four different plant extracts was screened against twelve pathogenic microorganisms and two reference bacterial strains. Methanolic extracts of Oxalis corniculata, Artemisia vulgaris, Cinnamomum tamala, and Ageratina adenophora were subjected to a test of their antimicrobial properties by agar well diffusion method. The result indicated that most of the extracts exhibited antimicrobial properties. The highest potential was observed in the extract of O. corniculata against Escherichia coli, Salmonella Typhi, MDR Salmonella Typhi, Klebsiella pneumoniae, and Citrobacter koseri with zone of inhibition (ZOI) of 17 mm, 13 mm, 16 mm, 11 mm, and 12 mm, respectively. Oxalis corniculata also showed the highest MIC against test organisms. The methanolic extract of Artemisia vulgaris, Cinnamomum tamala, and Ageratina adenophora showed efficacy against Staphylococcus aureus. Ageratina adenophora also showed antifungal activity against Rhizopus spp. The experiment confirmed the efficacy of some selected plant extracts as natural antimicrobials and suggested the possibility of employing them in drugs for the treatment of infectious diseases caused by the test organisms.

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Raj Kumar Dahal

Papers

In Vitro Antimicrobial Activity of Some Medicinal Plants against Human Pathogenic Bacteria.