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Financial support: Project INIA-LIA 057, CSIC 308 and by the Maestría en Biotecnología, Facultad de Ciencias, Universidad de la República, Uruguay.

Silver nanoparticles have particular properties that contribute to their very promising applications, novel in various fields of science, such as the development of biosensors, the diagnosis and treatment of cancer, the controlled release of drugs and the antimicrobial potential. The biological synthesis of nanoparticles is of great interest over other physical and chemical methods because the use of toxic chemicals and drastic reaction conditions are avoided. The extracellular biosynthesis using fungi could also make downstream processing much easier than the intracellular biosynthesis. One of the main applications of silver nanoparticles is their antimicrobial activity. Several studies have demonstrated the bactericidal properties of silver nanoparticles are different from silver ions, and that they are strongly influenced by their shape, size, concentration and colloidal state. In the present work, the ability of fungal strains from Uruguay to synthesize silver nanoparticles was studied. Eight fungi were able to synthesize nanoparticles. An extensive physicochemical characterization of the nanoparticles was carried out including ultraviolet-visible spectroscopy, transmission electron microscopy, dynamic light scattering, zeta-potential and gel electrophoretic mobility. According to the characterization and colloidal stability results, nanoparticles from three fungi were selected for antimicrobial activity assays. All nanoparticles were able to inhibit Escherichia coli growth, demonstrating their potential as effective antibacterial agent for use in biomedical applications.

Microorganisms offer an alternative green and scalable technology for the synthesis of value added products. Fungi secrete high quantities of bioactive substances, which play dual-functional roles as both reducing and stabilizing agents in the synthesis of colloidal metal nanoparticles such as silver nanoparticles, which display potent antimicrobial properties that can be harnessed for a number of industrial applications. The aim of this work was the production of silver nanoparticles using the extracellular cell free extracts of Phanerochaete chrysosporium, and to evaluate their activity as antimicrobial and antibiofilm agents. The 45–nm diameter silver nanoparticles synthesized using this methodology possessed a high negative surface charge close to −30 mV and showed colloidal stability from pH 3–9 and under conditions of high ionic strength ([NaCl] = 10–500 mM). A combination of environmental SEM, TEM, and confocal Raman microscopy was used to study the nanoparticle-E. coli interactions to gain a first insight into their antimicrobial mechanisms. Raman data demonstrate a significant decrease in the fatty acid content of E. coli cells, which suggests a loss of the cell membrane integrity after exposure to the PchNPs, which is also commensurate with ESEM and TEM images. Additionally, these biogenic PchNPs displayed biofilm disruption activity for the eradication of E. coli and C. albicans biofilms.

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