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Full Version: Silver Nanoparticle: An Antifungal Agent
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Introduction:
Bio-nanotechnology is used for developing biosynthesis and environmental-friendly technology for synthesis of nanomaterials and nanoparticles. Nano particles are considered as a powerful tool to develop new approaches in the field of designing new antimicrobial drugs. Nowadays fungal infections resulted from opportunistic fungi have been common especially in people talented in being affected by special conditions like immune weakness , pregnancy and diseases like HIV and the candidates of affection to these infections. As like the bacterial stains, fungal stains also developed their resistence to antifungal drug. Now days several types of nanomaterials like copper, zinc, titanium, magnesium, gold, alginate and silver are used. Silver or silver ions have long been known to have strong inhibitory and bactericidal effect as well as a broad spectrum of antimicrobial activities. The current investigation supports the theory that the use of silver ions or metallic silver as well as Nano-Ag can be exploited in medicine for burn treatment, dental materials, and possesses low toxicity to human cells, high thermal stability and low volatility. Silver nanoparticles (NPs), shows a very strong bactericidal activity against both gram-positive and gram-negative bacteria including multi resistant strains. The antifungal effect of silver NPs has received only marginal attention and just a few studies on this topic have been published. Recent studies revealed the effects of silver NPs as antifungal agents. Recent studies also revealed that silver nanoparticles are comparatively better than other antibiotics which are currently used as antifungal agent.

Synthesis of nanoparticles

The silver nano particles can be synthesized either by biological or non-biological method. The biological method includes silver nanoparticle synthesis from bacteria (ex: Bacillus licheniformis), marine microalgae (ex: Isochrysis galbana), yeast (ex: MKY3), fungi (ex: Aspergillus flavus), plants (ex: Aloe Vera). At the stationary phase of the marine microalgal culture the 0.01 normality of the silver nitrate solution is added, the silver is reduced to silver nanoparticles. Exposure of the fungal biomass to aqueous Ag+ ions resulted in the intracellular reduction of the metal ions and formation of silver nanoparticles. Silver nanoparticles were synthesized extracellular by a silver-tolerant yeast strain MKY3, with 1 mmol L–1 soluble silver in the log phase of growth. In plants, the leaf extracts were treated with silver to synthesize the silver nanoparticles. The non-biological methods for the synthesis of silver nanoparticles are physical method and chemical method. The physical method includes physical vapor condensation, arc discharge method. The chemical methods include chemical reduction, photochemical method, electrochemical method (electrolysis), and pyrolysis.


Antifungal activity of silver nanoparticles

Fungi are usually saprophytic. Once they enter the host cells it becomes parasite. Fungi often develop morphogenetic virulence mechanisms, e.g., formation of yeasts, hyphae, and spherules that facilitate their multiplication within the host. The transition of the fungi yeast to the mycelial growth in the host cell is said to be the dimorphic transition. This transition is responsible for pathogenicity in the host cells. In order to find the antifungal activity of the silver nano particles the dimorphic transition of the fungi was investigated. A mycelial form can be induced by temperature, pH, and serum. Silver nanoparticles attach to cell membrane and penetrate in the fungi then produce a site witch little molecular weight in center of fungi, and then Silver nanoparticles attach to respiratory sequence and finally cell division stop lead to cell death, Silver nanoparticles release silver ion in fungal cell which increase antifungal function as result. The serum-induced mycelia were significantly inhibited from extending and forming in the presence of Silver nanoparticles but the mycelia formed was normal in the absence of Nano-Ag.

Antifungal effect of silver nanoparticles

The antifungal effect of the silver nanoparticles is identified by various methods depends on the fungal species. One of the most commonly used method in the broth dilution method. The broth dilution method is used for identification of the minimum inhibitory concentration (MIC). The 80% inhibitory concentration (IC80) was defined as the lowest concentration that inhibited 80% of the growth as determined by a comparison with the growth in the control. MIC was found for silver nanoparticles and also for the antifungal drugs such as fluconazole, amphotericin B, geriscofalvin. Anti-fungal drug fluconazole is more effective than the amphotericin B. the inhibitory concentrations of silver nanoparticle and marketly available antibiotics were found at 50, 80, 90% of concentrations. On an average of these inhibitory concentrations of Amphotericin B, Fluconazole, geriscofalvin, silver nanoparticles were 16mg/ml, 64mg/ml, 8mg/ml, and 4 mg/ml respectively. This it shows that silver nanoparticles is more effective than the marketly available chemical antifungal drugs. The changes in the cell structure of the fungi due to the silver nanoparticles are viewed and identified by scanning electron microscopy or transmission electron microscopy. This shows “pits” in the cell membrane of the fungus due to action of silver nanoparticles which leads to the cell death. This method is double attenuated method.

Along with the anti-fungal activity, the hemolytic activities of the silver nanoparticles against the human erythrocytes are also determined. Many antimicrobial agents are limited regarding clinical applications, as they can induce cytolysis of human cells. The hemolytic activity of Nano-Ag was investigated as an indicator of its cytotoxicity to mammalian cells. The hemolytic activity is measured by the release of hemoglobin from the 4% suspension of the human red blood cells. Hemolytic effect of silver nanoparticles is compare with the chemical antifungal drugs such as amphotericin B. it is found that silver nanoparticle caused 6% lists of erythrocyte whereas amphotericin B induced 10% lysis. This proves that Silver nanoparticle could be applied to therapeutic agents regarding human fungal diseases with low cytotoxicity. This can act as broad spectrum antifungal agent. Silver nanoparticles exhibited potent antifungal effects on fungi tested, probably through destruction of membrane integrity; therefore, it was concluded that silver nanoparticles has considerable antifungal activity, deserving further investigation for clinical applications.