Also, antimicrobial and antifungal activities have been reported [ 34 ]. Complex coacervation A distinct attempt of providing improved properties for natural extracts by hybrid processing was involving complex coacervation. The extract used was that of propolis, already known as a natural-source food additive. Isolated pectin and soy protein were used as encapsulation material. Although the compounds used in encapsulation were of natural origin, isolation of compounds and the complex coacervation protocol represented a step forward in improving the properties of nanomaterials by encapsulation.
The authors have demonstrated the technology to generate a stable, alcohol-free agent in a powder formulation that elicits controlled release properties, but also demonstrated antimicrobial activity against Staphylococcus aureus [ 35 ]. Polymer-based encapsulation and liposomes However, most researchers have focused toward synthetic, polymer-based systems as well as liposomes.
The need for packaging food using materials with antibacterial properties motivated the work of a research team who designed nanocapsules with cinnamaldehyde. Immobilization on glass slide was further performed and this type of product demonstrated significant antibacterial activity against E. The efficacy of liposomes containing cinnamon natural extracts against methicillin-resistant Staphylococcus aureus MRSA was also demonstrated in a recent article and was appreciated as satisfactory by the team.
As colony forming unit determination reveals, such formulation could offer high efficiency against MRSA biofilms on various classes of substrates, from steel, nonwoven fabrics, gauze, and up to nylon membranes. The formulation was demonstrated to augment stability of antibacterial effect and to prolong the period of action [ 37 ]. Similarly, Fennel extract was encapsulated by another center, in the attempt to create food additives able to exert antimicrobial role on the fish meat carp species.
The extract demonstrated antioxidant effects, as well an antibacterial effect as revealed by the microbial count. The efficacy of the liposome-encapsulated form proved superior in terms of oxidative deterioration to tissues and reducing of microbial colonization.
The formulation also provided extended shelf life following treatment of carp fillet [ 38 ]. Another recent report also demonstrated superior antioxidant and antimicrobial properties of Thymus species extracts. The team obtained an enriched antioxidant activity and antimicrobial effect of the liposomes containing extracts coming from the four selected species of Thymus as compared to the extract alone [ 39 ].
The growth inhibition of E. Driven conclusions were equally sustained by a distinct research group, who finds the phytosomes as suitable for drug and food applications, their stability, physicochemical properties, and antibacterial efficiency being dependent of specific method of synthesis. The liposomal encapsulation is considered as preserving the activity of bioactive components as compared to water solution, this particularity being caused by the elevated water solubility and reduced lipid solubility [ 41 ].
A more extensive study tested various encapsulation designs for active components such as lysozyme, nisin as well as various herbs and spice extracts, including liposomal, chitosan as well as polysaccharide encapsulation. The advantage of liposomal formulation could come from their higher stability compared to chitosan encapsulation. Antimicrobial activity against both positive and negative of Gram bacteria was efficient and stable for a minimum of 1 month. Due to the controlled release possibility derived from the formulation concept, the authors indicate a large potential for applications under hydrogel form with embedded capsules containing natural extracts [ 42 ].
Recently, the synthesis protocols became more oriented toward complex structures, such as polymer-lipid nanoparticles. One of the most robust designs is represented by a core-shell concept, presenting a polymeric core, a lipid shell with embedded active substance, and protected by polyethylene-glycol moieties for immunoreactivity reduction [ 43 ]. The advantages of such structures come from increased stability, morphological and structural integrity, low risk of damage during storage, controlled release features, elevated biocompatibility, and bioavailability.
Both the polymeric and the lipidic component can be built using not only artificial, but also using natural sources, such as chitosan or natural fatty acids and represent the next generation of materials directed toward antimicrobial applications [ 44 ]. Nanoparticles functionalized with natural biomolecules Not all research groups have followed the encapsulation trend. A part of the research teams have focused on direct attachment of biologically active, natural origin molecules onto the surface of metal nanoparticles.
One such design was the synthesis of catechin-Cu nanoparticles. Similarly, iron oxide nanoparticles were functionalized with natural source gallic acid. The resulting construct was demonstrating significant antibacterial effect against E. Also, chitosan, a natural polysaccharide, was demonstrated as presenting improved efficiency when binded to copper or zinc nanoparticles, and the effect has been published to be proportional to the level of zeta potential [ 47 ].
Silver nanoparticles were also reported to have been successfully functionalized with glucosamine, a natural sugar.
The newly constructed compound presented high antimicrobial efficiency. Both Klebsiella pneumoniae and Bacillus cereus were more sensitive to the functionalized as compared to pristine AgNps, as demonstrated by minimum inhibitory concentration determination [ 48 ]. Research has been advancing toward ore and more complex designs. In another publication, a crosslinked chitosan-coated Ag-loaded nano-SiO2 composite was reported to exert a good antimicrobial activity against S.
Another biofilm-destructive solution was that of polysaccharide-bound silver nanoparticles. Green synthesis of caboxy-methyl-tamarind, polysaccharide-capped silver nanoparticles was performed, and the newly designed construct has demonstrated inhibitory effects against E. The obtained effect could be efficient against bacterial biofilm formation and consolidation [ 50 ]. Mechanisms underlying the antimicrobial effect of natural-synthetic hybrid materials Although consistent efforts have been made for development of hybrid, natural-synthetic designs, as well as testing their antimicrobial effects, there is still limited data regarding the exact mechanisms involved in the obtained antimicrobial effects.
However, the natural compound in the construct can be considered as an important contributor in the final bacterial inhibition mechanism. The most important antimicrobial mechanisms involved in natural extract action, along with studies detailing the effect, are summarized below. Membrane permeabilization, membrane potential alterations, and cellular component leakage One of the most incriminated antimicrobial mechanisms used by natural extracts involves the functional and structural integrity of the membrane.
Leucas aspera, Hemidesmus indicus, and Plumbago zeylanica ethanolic extracts revealed different mechanisms of membrane functional attack. While data on the ethanolic extracts of Hemidesmus indicus and Plumbago zeylanica revealed disruption of membrane continuity with leakage of cellular content and consecutive alteration of membrane potential, extract of Leucas aspera demonstrated functional alteration properties, with limited anatomical destruction consecutive to exposure.
The latter was found to generate inner membrane alterations with preservation of outer membrane continuity, therefore lacking complete permeabilization. The effects were studied on E. Authors provided evidence on green emission fluorochrome leakage as well as electron microscopy evidences of membrane blebbing with release of cellular contents.
Such events could be possibly explained by the presence of flavonoid and phenol antioxidant molecules in the extracts, known to exert a detergent-like effect. Moreover, the antimicrobial effects were proven to be dependent on concentration and time [ 51 ]. The extract induced significant morphological changes such as: membrane rupturing, and content release into the exterior all followed by cell death, as images provided by scanning electron microscope have revealed [ 52 ]. Detailed evidences of protein leakage were brought by a distinct research group, while testing the effects of Cocos nucifera extract.
The effects after bacterial exposure were analyzed from the minimal inhibitory concentration, protein potassium ions leakage from cells as well as nucleotide release following membrane permeabilization. Results demonstrate significant antimicrobial effects. Calculated MIC was ranging between 0. In a similar manner, the assessment of the effects exerted by Veronica montana L.
Various bacterial strains, including Gram-positives and Gram-negatives were tested, by monitoring their sensitivity to exposure to extract. The most sensitive strain has been L. Also, another research group has studied the effects of monocaprylate, as a naturally generated molecule. The team focused on the mechanisms underlying the death induced by monocaprylate on different strains, such as E. Cell morphology and content, as well as continuity of membrane were examined. Different methods, such as atomic force microscopy and propidium iodide staining, were used to depict the mechanisms.
Also, by means of quartz crystal microbalance measurements, the authors have measured the concentration of monocaprylate in the samples. Based on obtained data and theoretical considerations, the authors have reasoned that the sensitivity of the membrane itself plays a role in the molecule-membrane interaction. Lipidic componence, fluidity of membrane as well as the sphericity of the membrane may play an important role.
It has been demonstrated that the destructuring of membrane by the chosen testing molecule is done by increasing the amount of membrane and the fluidity level [ 55 ].
Moreover, in a recent study, intensive oxygen reactive species generation, with consecutive membrane destabling and protein leakage, was found following exposure of Salmonella typhimurium as well as other strains to the methanolic extract of Scutellaria barbata S.
The mechanisms resulted in a Alterations in regulation of gene expression The release of bacterial cell content as a result to treatment-induced permeabilization is preceded by enhanced expression of different proteins. The paper suggests common antibacterial routes for different natural antimicrobial treatments [ 57 ]. Altering bacterial communication, exerted by plant natural therapies was demonstrated by qRT-PCR and was reported to be induced by down-regulation of quorum-sensing already established genes [ 58 ].
Metabolic alterations Besides the already discussed mechanisms, a recent paper has discussed the addition of metabolic-induced alterations by exposure to natural extracts. The mechanisms identified by the authors were respiratory enzymatic inhibition, inducement of oxidative stress, heat-shock state, and forcement of bacterial acute stringent response. The ATP level tends to decrease in the cell, as demonstrated by the E. Effects induced by nanoparticles The antimicrobial effect of particular nanomaterials represents a complex interaction of distinct effects.
Modulation of effects could theoretically come from the cell internalization of free ions resulting from the nanomaterials, cell-nanostructure interaction, and physical properties of the nanostructures such as dimension, morphology, or surface charge. Due to the large area provided by the surface of nanoparticle, the different chemical nature of nanostructures and the final effects are hard to predict and therefore represent a serious research aim for each individual type of nanomaterial [ 60 ].
Among antibacterial applications, silver nanoparticles represent a major fraction of tested materials due to widely accepted and traditionally known effects of silver.
The AuNPs were of spherical, triangular and irregular shapes with an average size of AuNPs were distributed in the cell envelope, across the cytosol and in the extracellular space. Biosynthesis of AuNPs was optimized with respect to the initial concentration of gold salt, bacterial growth period, solution pH and temperature.
The purified AuNPs exhibited significant antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria by damaging their cytoplasmic membrane. Therefore, the extreme bacterium D. Compared with bulk gold materials, AuNPs with nanoscale size and morphological properties have unique characteristics including physical, chemical, electrical, mechanical, magnetic, optical and biological properties.
However, consumption of high levels of energy during the physical process and use of plenty of chemicals as well as generation of potential hazardous waste during the chemical process limit the applications of these processes. Biosynthetic process for nanoparticles using microorganisms and plants is receiving increasing attention due to its milder process condition and reduced use of toxic chemicals and has been suggested as a valuable alternative to physical and chemical methods. Deinococcus radiodurans, a red-pigmented nonpathogenic bacterium isolated from an irradiated meat can, 18 is well known for its exceptional resistance to radiation 15, Gy of ionizing radiation without lethality and oxidants.
The survival strategies of D. Moreover, the cellular envelope of D. Moreover, AuNPs have significant potential in biomedical applications due to their biocompatibility and chemical inertness to mammalian cells, 5 — 7 compared with the relatively toxic silver nanoparticles, which can induce argyrism. In the present study, the ability of D. The AuNPs synthesized by D.
The mechanism of Au speciation and reduction by the bacterium was analyzed by X-ray photoelectron spectroscopy XPS. The antibacterial activity of AuNPs as shown by cytomembrane damage in the Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium E.
Materials and methods Bacterial cultures and chemicals D. Bacterial growth was assessed by measuring optical density OD at nm for D. All reagents used were of analytical grade. The pH of each working solution was adjusted by hydrochloric acid or sodium hydroxide. Chloramphenicol was used as a control in the antibacterial assays. Identification and dynamic analysis of AuNPs formation D. The absorption spectra of sample aliquots from to nm were recorded as a function of reaction time.
The reaction time was 8 h.The future of research within the discussed topic is dependent on improved mechanistic understanding at the interface between material and bacterial cell, as well as more in depth knowledge on nanomaterials and their specific behavior in different conditions. The effects after bacterial exposure were analyzed from the minimal inhibitory concentration, protein potassium ions leakage from cells as well as nucleotide release following membrane permeabilization. The need for packaging food using materials with antibacterial properties motivated the work of a research team who designed nanocapsules with cinnamaldehyde. Moreover, the cellular envelope of D. The team demonstrates strong near-infrared absorbance, suggesting a good potential for hyperthermia-modulated applications, such as anticancer or antimicrobial effects [ 20 ]. Based on obtained data and relevant considerations, the authors have used that the sensitivity of the membrane itself examples a role in the environment-membrane interaction. The factory was demonstrated to generate stability of antibacterial low and to prolong the different of action [ 37 ]. Preparation of AuNPs explaining D.
In the new green synthesis concept, any traces, if present, would be a part of a natural compound with rather beneficial than dangerous effects. Nanotechnology potential in antimicrobial therapy is increasingly demonstrated by various data. One such report is the synthesis of silver nanoparticles using Acorous calamus rhizome extract.
Reducing or stabilizing agents could be good examples of such traces. The whole-plant extract of Boerhavia diffusa involved collection, washing of plant, drying, followed by Soxhlet apparatus-based extraction and power formulation by reducing under pressure. Another biofilm-destructive solution was that of polysaccharide-bound silver nanoparticles. Also, chitosan, a natural polysaccharide, was demonstrated as presenting improved efficiency when binded to copper or zinc nanoparticles, and the effect has been published to be proportional to the level of zeta potential [ 47 ].
The construct demonstrated biofilm-destructive properties as well as direct antibacterial effects against methicillin-resistant Staphylococcus aureus. Cyclodextrin encapsulation Increasing the efficiency of natural compounds as well as diminishing their drawbacks, such as limited bioavailability or excessive rate of release, has been one major and constant research topics during late years. Both the polymeric and the lipidic component can be built using not only artificial, but also using natural sources, such as chitosan or natural fatty acids and represent the next generation of materials directed toward antimicrobial applications [ 44 ]. Recently, the synthesis protocols became more oriented toward complex structures, such as polymer-lipid nanoparticles. A part of the research teams have focused on direct attachment of biologically active, natural origin molecules onto the surface of metal nanoparticles.
Biosynthesis of AuNPs was optimized with respect to the initial concentration of gold salt, bacterial growth period, solution pH and temperature. The antibacterial activity and mobilization of AuNPs were also analyzed using the agar diffusion test.