Biosynthesis of silver nanoparticles by the endophytic fungus Epicoccum nigrum and their activity against pathogenic fungi

Synthesis of Silver Nanoparticles Mediated by Fungi: A Review

The use of fungi as reducing and stabilizing agents in the biogenic synthesis of silver nanoparticles is attractive due to the production of large quantities of proteins, high yields, easy handling, and low toxicity of the residues. Furthermore, this synthesis process coats the nanoparticles with biomolecules derived from the fungus, which can improve stability and may confer biological activity. The aim of this review is to describe studies in which silver nanoparticles were synthesized using fungi as reducing agents, discussing the mechanisms and optimization of the synthesis, as well as the applications. The literature shows that various species of fungus have potential for use in biogenic synthesis, enabling the production of nanoparticles with different characteristics, considering aspects such as their size, surface charge, and morphology. The synthesis mechanisms have not yet been fully elucidated, although it is believed that fungal biomolecules are mainly responsible for the process. The synthesis can be optimized by adjusting parameters such as temperature, pH, silver precursor concentration, biomass amount, and fungus cultivation time. Silver nanoparticles synthesized using fungi enable the control of pathogens, with low toxicity and good biocompatibility. These findings open perspectives for future investigations concerning the use of these nanoparticles as antimicrobials in the areas of health and agriculture.

Are Fungal Endophytes Merely Mycorrhizal Copycats? The Role of Fungal Endophytes in the Adaptation of Plants to Metal Toxicity

The contamination of soil with toxic metals is a worldwide problem, resulting in the disruption of plant vegetation and subsequent crop production. Thus, remediation techniques for contaminated soil and water remain a constant interest of researchers. Phytoremediation, which utilizes plants to remove or stabilize contaminants, is perceived to be a promising strategy. However, phytoremediation's use to date is limited because of constraints associated with such factors as slow plant growth rates or metal toxicity. Microbial-assisted phytoremediation serves as an alternative solution, since the impact of the microbial symbionts on plant growth and stress tolerance has frequently been described. Endophytic fungi occur in almost every plant in the natural environment and contribute to plant growth and tolerance to environmental stress conditions. Although this group of symbiotic fungi was found to form association with a wide range of hosts, including the non-mycorrhizal Brassicaceae metallophytes, their role in the response of plants to metal toxicity has not been thoroughly elucidated to date. This review summarizes the current knowledge regarding the role of endophytic fungi in the tolerance of plants to toxic metals and highlights the similarities and differences between this group of symbiotic fungi and mycorrhizal associations in terms of the survival of the plant during heavy metal stress.

The biotechnological potential of Epicoccum spp.: diversity of secondary metabolites

Epicoccum is a genus of ubiquitous fungi typically found in air, in soil, and on decaying vegetation. They also commonly display an endophytic lifestyle and are isolated from diverse plant tissues. The fungi from the genus Epicoccum are mainly known for their use as biocontrol agents against phytopathogens and for their ability to produce many secondary metabolites with potential biotechnological applications, such as antioxidant, anticancer,r and antimicrobial compounds. Among the bioactive compounds produced by Epicoccum spp., epicocconone is a commercially available fluorophore, D8646-2-6 is a patented telomerase inhibitor, and taxol is an anticancer drug originally isolated from Taxus brevifolia. Epicoccum spp. also produces epicolactone, an antimicrobial compound with a unique and complex structure that has aroused considerable interest in the chemical-synthesis community. The main goal of the present review is to discuss the diversity of secondary metabolites produced by Epicoccum spp., their biotechnological applications, and proposed hypothetical biosynthesis. In addition, the use of Epicoccum spp. as biocontrol agents and the pigments produced by these fungi are also discussed.

Biological synthesis and characterisation of silver nanoparticles using Pseudomonas geniculata H10 for pharmaceutical activity

In the present study, silver nanoparticles (SNPs) were synthesised for the first time using Pseudomonas geniculata H10 as reducing and stabilising agents. The synthesis of SNPs was the maximum when the culture supernatant was treated with 2.5 mM AgNO3 at pH 7 and 40°C for 10 h. The SNPs were characterised by field emission scanning electron microscopy-energy-dispersive spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray diffraction and UV-vis spectroscopy. Fourier transform infrared spectroscopy indicated the presence of proteins, suggesting they may have been responsible for the reduction and acted as capping agents. The SNPs displayed 1,1-diphenyl-2-picrylhydrazyl (IC50 = 28.301 μg/ml) and 2,2'-azinobis-3-ethylbenzothiazoline-6-sulphonate (IC50 = 27.076 μg/ml) radical scavenging activities. The SNPs exhibited a broad antimicrobial spectrum against several human pathogenic Gram-positive and Gram-negative bacteria and Candida albicans. The antimicrobial action of SNPs was due to cell deformation resulting in cytoplasmic leakage and subsequent lysis. The authors' results indicate P. geniculata H10 could be used to produce antimicrobial SNPs in a facile, non-toxic, cost-effective manner, and that these SNPs can be used as effective growth inhibitors in various microorganisms, making them applicable to various biomedical and environmental systems. As far as the authors are aware, this study is the first to describe the potential biomedical applications of SNPs synthesised using P. geniculata.

Production of bioproducts by endophytic fungi: chemical ecology, biotechnological applications, bottlenecks, and solutions

Endophytes are microorganisms that colonize the interior of host plants without causing apparent disease. They have been widely studied for their ability to modulate relationships between plants and biotic/abiotic stresses, often producing valuable secondary metabolites that can affect host physiology. Owing to the advantages of microbial fermentation over plant/cell cultivation and chemical synthesis, endophytic fungi have received significant attention as a mean for secondary metabolite production. This article summarizes currently reported results on plant-endophyte interaction hypotheses and highlights the biotechnological applications of endophytic fungi and their metabolites in agriculture, environment, biomedicine, energy, and biocatalysts. Current bottlenecks in industrial development and commercial applications as well as possible solutions are also discussed.

Pleurotus sajor-caju can be used to synthesize silver nanoparticles with antifungal activity against Candida albicans

BACKGROUND

Green synthesis of silver nanoparticles (AgNPs) has become widely practiced worldwide. In this study, AgNPs were synthesized using a hot-water extract of the edible mushroom Pleurotus sajor-caju. The product, PSC-AgNPs, was characterized by using UV-visible spectra, dynamic light scattering analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectrometry. To assess its antifungal activity against Candida albicans, gene transcription and protein expression analyses were conducted for CaICL1 and its product, ICL, using real-time quantitative polymerase chain reaction and western blot, respectively.

RESULTS

PSC-AgNPs with an average particle size of 11.68 nm inhibited the growth of the pathogenic yeast C. albicans. Values for minimum inhibitory concentration and minimum fungicidal concentration were 250 and 500 mg L^-1 , respectively. TEM images revealed that the average particle size of PSC-AgNPs was 16.8 nm, with the values for zeta potential and the polydispersity index being -8.54 mV and 0.137, respectively. XRD and FTIR spectra showed PSC-AgNPs to have a face-centered cubic crystalline structure. The polysaccharides and amino acid residues present in P. sajor-caju extract were found to be involved in reducing Ag⁺ to AgNP. Both CaICL1 transcription and ICL protein expression were found to be suppressed in the cells treated with PSC-AgNPs as compared with the control.

CONCLUSION

Our PSC-AgNP preparation makes for a promising antifungal agent that can downregulate isocitrate lyase. © 2017 Society of Chemical Industry.

Mycosynthesis of bactericidal silver and polymorphic gold nanoparticles: physicochemical variation effects and mechanism

AIM

Extracellular synthesis of silver and gold nanoparticles using aqueous cell-free filtrate (CFF) of endophytic Chaetomium globosum and characterization of its bioactive proteins.

METHODS

Temperature and pH gradients were used to assess their effects on dimensions of NPs. NPs were tested in vivo for antibacterial activity. MALDI-TOF-MS/MS was used for characterization of CFF proteins.

RESULTS

Fungal CFF fabricated nanoparticles of various shape under varied physicochemical conditions. Silver nanoparticles showed significantly (p ≤ 0.5) enhanced antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae compared with AgNO₃. Two prominent CFF proteins showed homology with benzoate 4-monooxygenase cytochrome P450 and ubiquinol-cytochrome c reductase.

CONCLUSION

The study achieved controlled mycosynthesis of NPs and explains the hitherto poorly known mechanism of reduction, stabilization and antibacterial activity of nanoparticles.

Biosynthesis of nanosilver using Chaetomium globosum and its application to control Fusarium wilt of tomato in the greenhouse

Fusarium wilt of tomato (Lycopersicon esculentum ) caused by Fusarium oxysporum f. sp. lycopersici is one of the most important diseases that affect this crop worldwide. This study aimed to biosynthesise nanosilver (AgNPs) using Chaetomium globosum , to evaluate its in vitro antifungal activity against pathogenic F. oxysporum and in vivo control of tomato seedlings wilt in the greenhouse. AgNPs was tested for its in vitro antifungal potential against F. oxysporum using poisoned food technique on three different growth media, agar well diffusion assay, inhibition of colony formation (CFU), and tested for its potency to control seedlings wilt upon its use at different concentrations (50, 100 and 500 mg/l) and for different incubation periods (0, 1, 2 and 4 h). Results indicated that C. globosum succeeded to biosynthesise AgNPs with maximum UV/vis absorbance around 420–450 nm, spherical in shape with particle size of 11–14 nm according to Transmittance electron microscope and displayed high purity recorded through X‐ray diffraction (XRD). In vitro studies revealed high antifungal activity of AgNPs against F. oxysporum noticed especially at a concentration of 500 mg/l and after incubation period for 4 h. The CFU of F. oxysporum on potato dextrose agar (PDA) medium decreased significantly on increasing the concentration and time of incubation with AgNPs. In the greenhouse, AgNPs caused appreciable enhancement in the growth parameters of tomato seedlings such as; root, shoot fresh weight, and height of seedlings in soil infested with F. oxysporum compared with the control. In addition, AgNPs reduced the severity of wilt disease by 90% observed through decreasing the number of wilted seedlings especially after placing their roots in 500 mg/l of AgNPs suspension for 4 h prior to soil infestation with the pathogen. This study recorded for the first time that C. globosum has the ability to synthesise AgNPs which showed significant in vivo antifungal potential observed through control of Fusarium wilt of tomato seedlings, in addition to enhancing their growth parameters in the greenhouse.

Antibacterial Activity of Silver Nanoparticles against Staphylococcus warneri Synthesized Using Endophytic Bacteria by Photo-irradiation

Diseases caused by Staphylococcus warneri have a significant impact on human health. We evaluated the antibacterial activity of silver nanoparticles (synthesized using the endophytic strain SYSU 333150) against S. warneri. The strain SYSU 333150 was isolated from the roots of Borszczowia aralocaspica Bunge. The 16S rRNA sequence results suggest that SYSU 333150 belongs to the genus Isoptericola and is likely a new species. Photo-irradiation was used to synthesize silver nanoparticles, which were characterized using UV-visible spectroscopy, transmission electron microscopy and X-ray diffraction. The nanoparticles were spherical and measured to be11 to 40 nm. X-ray diffraction revealed four peaks corresponding to the 111, 200, 220, and 311 planes of the face-centered cubic lattice, indicating a crystalline nature. Fourier transform infrared spectroscopy suggested that the metabolites in the culture supernatant were likely reducing and capping agents. The silver nanoparticles possessed antimicrobial activity (14 mm zone of inhibition) against S. warneri, which was likely a result of DNA cleavage. The synthesized silver nanoparticles have potent antibacterial activity against S. warneri and can be used to control infection.

Applying Taguchi design and large-scale strategy for mycosynthesis of nano-silver from endophytic Trichoderma harzianum SYA.F4 and its application against phytopathogens

Development of reliable and low-cost requirement for large-scale eco-friendly biogenic synthesis of metallic nanoparticles is an important step for industrial applications of bionanotechnology. In the present study, the mycosynthesis of spherical nano-Ag (12.7 ± 0.8 nm) from extracellular filtrate of local endophytic T. harzianum SYA.F4 strain which have interested mixed bioactive metabolites (alkaloids, flavonoids, tannins, phenols, nitrate reductase (320 nmol/hr/ml), carbohydrate (25 μg/μl) and total protein concentration (2.5 g/l) was reported. Industrial mycosynthesis of nano-Ag can be induced with different characters depending on the fungal cultivation and physical conditions. Taguchi design was applied to improve the physicochemical conditions for nano-Ag production, and the optimum conditions which increased its mass weight 3 times larger than a basal condition were as follows: AgNO3 (0.01 M), diluted reductant (10 v/v, pH 5) and incubated at 30 °C, 200 rpm for 24 hr. Kinetic conversion rates in submerged batch cultivation in 7 L stirred tank bioreactor on using semi-defined cultivation medium was as follows: the maximum biomass production (Xmax) and maximum nano-Ag mass weight (Pmax) calculated (60.5 g/l and 78.4 g/l respectively). The best nano-Ag concentration that formed large inhibition zones was 100 μg/ml which showed against A.alternate (43 mm) followed by Helminthosporium sp. (35 mm), Botrytis sp. (32 mm) and P. arenaria (28 mm).

Mycoendophytes as efficient synthesizers of bionanoparticles: nanoantimicrobials, mechanism, and cytotoxicity

Mycoendophytes are the fungi that occur inside the plant tissues without exerting any negative impact on the host plant. They are most frequently isolated endophytes from the leaf, stem, and root tissues of various plants. Among all fungi, the mycoendophytes as biosynthesizer of noble metal nanoparticles (NPs) are less known. However, some reports showing efficient synthesis of metal nanoparticles, mainly silver nanoparticles and its remarkable antimicrobial activity against bacterial and fungal pathogens of humans and plants. The nanoparticles synthesized from mycoendophytes present stability, polydispersity, and biocompatibility. These are non-toxic to humans and environment, can be gained in an easy and cost-effective manner, have wide applicability and could be explored as promising candidates for a variety of biomedical, pharmaceutical, and agricultural applications. Mycogenic silver nanoparticles have also demonstrated cytotoxic activity against cancer cell lines and may prove to be a promising anticancer agent. The present review focuses on the biological synthesis of metal nanoparticles from mycoendophytes and their application in medicine. In addition, different mechanisms of biosynthesis and activity of nanoparticles on microbial cells, as well as toxicity of these mycogenic metal nanoparticles, have also been discussed.

Biomimetic Synthesis of Silver Nanoparticles Using Endosymbiotic Bacterium Inhabiting Euphorbia hirta L. and Their Bactericidal Potential

The present investigation aims to evaluate biomimetic synthesis of silver nanoparticles using endophytic bacterium EH 419 inhabiting Euphorbia hirta L. The synthesized nanoparticles were initially confirmed with change in color from the reaction mixture to brown indicating the synthesis of nanoparticles. Further confirmation was achieved with the characteristic absorption peak at 440 nm using UV-Visible spectroscopy. The synthesized silver nanoparticles were subjected to biophysical characterization using hyphenated techniques. The possible role of biomolecules in mediating the synthesis was depicted with FTIR analysis. Further crystalline nature of synthesized nanoparticles was confirmed using X-ray diffraction (XRD) with prominent diffraction peaks at 2θ which can be indexed to the (111), (200), (220), and (311) reflections of face centered cubic structure (fcc) of metallic silver. Transmission electron microscopy (TEM) revealed morphological characteristics of synthesized silver nanoparticles to be polydisperse in nature with size ranging from 10 to 60 nm and different morphological characteristics such as spherical, oval, hexagonal, and cubic shapes. Further silver nanoparticles exhibited bactericidal activity against panel of significant pathogenic bacteria among which Pseudomonas aeruginosa was most sensitive compared to other pathogens. To the best of our knowledge, present study forms first report of bacterial endophyte inhabiting Euphorbia hirta L. in mediating synthesizing silver nanoparticles.

Silver nanoparticle production by the fungus Fusarium oxysporum: nanoparticle characterisation and analysis of antifungal activity against pathogenic yeasts

The microbial synthesis of nanoparticles is a green chemistry approach that combines nanotechnology and microbial biotechnology. The aim of this study was to obtain silver nanoparticles (SNPs) using aqueous extract from the filamentous fungus Fusarium oxysporum as an alternative to chemical procedures and to evaluate its antifungal activity. SNPs production increased in a concentration-dependent way up to 1 mM silver nitrate until 30 days of reaction. Monodispersed and spherical SNPs were predominantly produced. After 60 days, it was possible to observe degenerated SNPs with in additional needle morphology. The SNPs showed a high antifungal activity against Candida and Cryptococcus , with minimum inhibitory concentration values ≤ 1.68 µg/mL for both genera. Morphological alterations of Cryptococcus neoformans treated with SNPs were observed such as disruption of the cell wall and cytoplasmic membrane and lost of the cytoplasm content. This work revealed that SNPs can be easily produced by F. oxysporum aqueous extracts and may be a feasible, low-cost, environmentally friendly method for generating stable and uniformly sized SNPs. Finally, we have demonstrated that these SNPs are active against pathogenic fungi, such as Candida and Cryptococcus .

Biosynthesis of silver nanoparticles by the fungus Arthroderma fulvum and its antifungal activity against genera of Candida, Aspergillus and Fusarium

The objective of this study was to find one or more fungal strains that could be utilized to biosynthesize antifungal silver nanoparticles (AgNPs). Using morphological and molecular methods, Arthroderma fulvum was identified as the most effective fungal strain for synthesizing AgNPs. The UV-visible range showed a single peak at 420 nm, which corresponded to the surface plasmon absorbance of AgNPs. X-ray diffraction and transmission electron microscopy demonstrated that the biosynthesized AgNPs were crystalline in nature with an average diameter of 15.5±2.5 nm. Numerous factors could potentially affect the process of biosynthesis, and the main factors are discussed here. Optimization results showed that substrate concentration of 1.5 mM, alkaline pH, reaction temperature of 55°C, and reaction time of 10 hours were the optimum conditions for AgNP biosynthesis. Biosynthesized AgNPs showed considerable activity against the tested fungal strains, including Candida spp., Aspergillus spp., and Fusarium spp., especially Candida spp.

Endogenic mediated synthesis of gold nanoparticles bearing bactericidal activity

The present investigation aimed to synthesize gold nanoparticles using Pseudomonas fluorescens 417 inhabiting Coffea arabica L. Biologically synthesized gold nanoparticles were polydispersed in nature and characterized using hyphenated techniques such as UV-visible spectrophotometry, which ascertained characteristic peaks between 450 nm and 650 nm. Fourier transform infrared analysis predicted the functional groups present in the cell-free supernatant that mediated the synthesis and stabilization of gold nanoparticles. The crystalline nature of the gold nanoparticles was analyzed with X-ray diffraction techniques that displayed the Bragg's diffraction intensity. Transmission electron microscopy revealed the size of nanoparticles ranging from 5 nm to 50 nm, with most of them bearing a spherical shape. The study also revealed the bactericidal activity of synthesized nanoparticles against a panel of clinically significant pathogens. Maximum activity was observed against Pseudomonas aeroginosa followed by Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Klebsiella pneumoniae. The results obtained in the present investigation are promising for ecofriendly approaches for synthesis of gold nanoparticles bearing bactericidal activity that can act as an alternative to combat drug-resistant pathogens.

Mycosynthesis of silver nanoparticles from Beauveria bassiana and its larvicidal, antibacterial, and cytotoxic effect on human cervical cancer (HeLa) cells

This paper deals with the synthesis, characterization and biological activities (mosquitocidal, antibacterial and cytotoxicity of cancer cells) of silver nanoparticles from the native entomopathogenic fungusBeauveria bassiana.

Extracellular synthesis of silver nanoparticles by novel Pseudomonas veronii AS41G inhabiting Annona squamosa L. and their bactericidal activity

In present investigation extracellular synthesis of silver nanoparticles were synthesized using cell free supernatant of Pseudomonas veronii AS41G isolated from Annona squamosa L. The bacterium significantly reduced silver nitrate to generate silver nanoparticles which was characterized with hyphenated techniques. Synthesis of silver nanoparticles preliminary confirmed by UV-Visible spectrophotometry with the intense peak at 410nm, Further FTIR analysis revealed the possible role of biomolecules in the supernatant responsible for mediating the nanoparticles formation. The XRD spectra exhibited the characteristic Bragg peaks of 100, 111, 200, and 220 facets of the face centred cubic symmetry of nanoparticles suggesting that these nanoparticles were crystalline in nature. TEM microgram showed polydispersity of nanoparticles with size ranging from 5 to 50nm. Synthesized silver nanoparticles showed antibacterial activity against human and environmental pathogens including MRSA. The study enlightens the role of biosynthesized silver nanoparticles as an emerging alternative for drug resistant microorganisms. The obtained results are promising enough to pave the environmentally benign nanoparticle synthesis processes without use of any toxic chemicals and also envision the emerging role of endophytes towards synthesis of nanoparticles. With scanty reports available on P.veronii species, a new role has been reported in this study which will be very valuable for future researchers working on it.

Highly efficient in vitro biosynthesis of silver nanoparticles using Lysinibacillus sphaericus MR-1 and their characterization

Silver nanoparticles (AgNPs) have been widely used in diverse fields due to their superior properties. Currently the biosynthesis of AgNPs is in the limelight of modern nanotechnology because of its green properties. However, relatively low yield and inefficiency diminish the prospect of applying these biosynthesized AgNPs. In this work, a rapid mass AgNP biosynthesis method using the cell-free extract of a novel bacterial strain, Lysinibacillus sphaericus MR-1, which has been isolated from a chemical fertilizer plant, is reported. In addition, the optimum synthesis conditions of AgNPs were investigated. The optimum pH, temperature, dosage, and reaction time were 12, 70 °C, 20 mM AgNO₃, and 75 min, respectively. Finally, AgNPs were characterized by optical absorption spectroscopy, zeta potential and size distribution analysis, x-ray diffraction, electron microscopy, and energy-dispersive x-ray spectroscopy. The results revealed that these biosynthesized AgNPs were bimolecular covered, stable, well-dispersed face centered cubic (fcc) spherical crystalline particles with diameters in the range 5-20 nm. The advantages of this approach are its simplicity, high efficiency, and eco-friendly and cost-effective features.

Mycosynthesis of silver nanoparticles bearing antibacterial activity

Mycosynthesis of silver nanoparticles was achieved by endophytic Colletotrichum sp. ALF2-6 inhabiting Andrographis paniculata. Well dispersed nanoparticles were characterized using UV–Visible spectrometry with maximum absorption conferring at 420 nm. FTIR analysis revealed possible biomolecules reducing the metal salt and stabilization of nanoparticles. XRD analysis depicted the diffraction intensities exhibiting between 20 and 80 °C at 2theta angle thus conferring the crystalline nature of nanoparticles. Morphological characteristic using TEM revealed the polydispersity of nanoparticles with size ranging from 20 to 50 nm. Synthesized nanoparticles exhibited bactericidal activity against selected human pathogens. Nanoparticles mode of action was carried out to reveal DNA damage activity. Thus the present investigation reports facile fabrication of silver nanoparticles from endophytic fungi.

Ultrastructures of silver nanoparticles biosynthesized using endophytic fungi

Three endophytic fungi Aspergillus tamarii PFL2, Aspergillus niger PFR6 and Penicllium ochrochloron PFR8 isolated from an ethno-medicinal plant Potentilla fulgens L. were used for the biosynthesis of silver nanoparticles. Scanning and transmission electron microscopic analysis were performed to study the structural morphology of the biosynthesized silver nanoparticles. The electron microscopy study revealed the formation of spherical nanosized silver particles with different sizes. The nanoparticles synthesized using the fungus A. tamarii PFL2 was found to have the smallest average particle size (3.5 ±3 nm) as compared to the nanoparticles biosynthesized using other two fungi A. niger PFR6 and P. ochrochloron PFR8 which produced average particle sizes of 8.7 ±6 nm and 7.7 ±4.3 nm, respectively. The energy dispersive X-ray spectroscopy (EDS) technique in conjunction with scanning electron microscopy was used for the elemental analysis of the nanoparticles. The selected area diffraction pattern recorded from single particle in the aggregates of nanoparticles revealed that the silver particles are crystalline in nature.

Evaluation of the antimicrobial potency of silver nanoparticles biosynthesized by using an endophytic fungus, Cryptosporiopsis ericae PS4

In the present study, silver nanoparticles (AgNPs) with an average particle size of 5.5 ± 3.1 nm were biosynthesized using an endophytic fungus Cryptosporiopsis ericae PS4 isolated from the ethno-medicinal plant Potentilla fulgens L. The nanoparticles were characterized using UV-visible spectrophotometer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), selective area electron diffraction (SAED), and energy dispersive X-ray (EDX) spectroscopy analysis. Antimicrobial efficacy of the AgNPs was analyzed singly and in combination with the antibiotic/antifungal agent chloramphenicol/fluconazole, against five pathogenic microorganisms--Staphylococcus aureus MTCC96, Salmonella enteric MTCC735, Escherichia coli MTCC730, Enterococcus faecalis MTCC2729, and Candida albicans MTCC 183. The activity of AgNPs on the growth and morphology of the microorganisms was studied in solid and liquid growth media employing various susceptibility assays. These studies demonstrated that concentrations of AgNPs alone between 10 and 25 μM reduced the growth rates of the tested bacteria and fungus and revealed bactericidal/fungicidal activity of the AgNPs by delaying the exponential and stationary phases. Examination using SEM showed pits and ruptures in bacterial cells indicating fragmented cell membrane and severe cell damage in those cultures treated with AgNPs. These experimental findings suggest that the biosynthesized AgNPs may be a potential antimicrobial agent.

Silver nanoparticles: therapeutical uses, toxicity, and safety issues

The promises of nanotechnology have been realized to deliver the greatest scientific and technological advances in several areas. The biocidal activity of Metal nanoparticles in general and silver nanoparticles (AgNPs) depends on several morphological and physicochemical characteristics of the particles. Many of the interactions of the AgNPs with the human body are still poorly understood; consequently, the most desirable characteristics for the AgNPs are not yet well established. Therefore, the development of nanoparticles with well-controlled morphological and physicochemical features for application in human body is still an active area of interdisciplinary research. Effects of the development of technology of nanostructured compounds seem to be so large and comprehensive that probably it will impact on all fields of science and technology. However, mechanisms of safety control in application, utilization, responsiveness, and disposal accumulation still need to be further studied in-depth to ensure that the advances provided by nanotechnology are real and liable to provide solid and consistent progress. This review aims to discuss AgNPs applied in biomedicine and as promising field for insertion and development of new compounds related to medical and pharmacy technology. The review also addresses drug delivery, toxicity issues, and the safety rules concerning biomedical applications of silver nanoparticles.