Silver nanoparticles: Fungi to beat bacteria

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  • Published: Apr 1, 2017
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Silver nanoparticles: Fungi to beat bacteria

Caning bacteria

Sugarcane plantation. Screening of filamentous fungi from sugarcane plantation soil for antimicrobial silver nanoparticles synthesis

Researchers in Brazil and the UK have used UV–Vis spectroscopy, scanning electron microscopy, EDX, and XRD to characterise silver nanoparticles made by soil fungi, with the potential to defeat antibiotic resistant bacteria.

Antibiotic resistance is an inevitable consequence of evolution by natural selection: in any given bacterial broth attacked with an antibiotic there will be present some bacteria that have a genetic mutation that makes them less susceptible to the otherwise lethal effects of the antibiotic. Those with such a mutation will survive the attack with the medicinal chemical weapon and will generate offspring that inherit the resistance. This was known from the first use of antibiotics. However, in recent decades the problem has grown for many reasons, not least antibiotic over-use in medicine, livestock management and the emergence of particularly virulent strains of microbes that can share genes with others on which they then confer resistance too. As such, our arsenal of effective drugs to treat bacterial, and fungal, infections is dwindling.

Particular particulates

New approaches to treating infection are needed urgently otherwise we may well be heading for a second visit to the era before antibiotics where a seemingly trivial infection could kill. One area in which research is showing promise is in antibiotic silver nanoparticles. Silver has been known to have bactericidal properties for many years. They are used in prosthetics bone, surgical instruments to reduce infection, in fashion clothes and footwear production as indirect deodorants that preclude bacterial growth, they are used in the beauty industry in conditioners and toothpaste, and in the clinical as topical treatment for wounds and infections. However, ingesting a silver sixpence is not a tenable method of administering the element to treat an internal infection. Instead, nanoparticles of the metal are being considered that would be able to reach the parts other approaches may well not.

Making silver nanoparticles with particular characteristics of biocompatibility, for instance, so that they might be absorbed is difficult. Now, writing in the journal AMB Express, Cristiane Angélica Ottoni of the Biosciences Institute, at São Paulo State University-UNESP in Brazil, Marta Filipa Simões of Edge Hill University, Ormskirk, Sara Fernandes of Richmond Pharmacology Ltd, St George’s University London, UK, Jonas Gomes dos Santos, Elda Sabino da Silva, and Alfredo Eduardo Maiorano of the Instituto de Pesquisa Tecnológica do Estado de São Paulo, and Rodrigo Fernando Brambilla de Souza of the Universidade Federal do Amazonas, Brazil, may have unearthed a solution.

Soil screen

The team explains how they have screened a batch of twenty different filamentous fungal strains taken from soil samples on a sugar cane plantation with the aim of identifying any that might be able to biosynthesise silver nanoparticles. Fundamentally, fungi have the greatest tolerance for accumulating metals compared even to plants and offer a possible environmentally benign biosynthesis for mass production of the needed silver nanoparticles. It has previously been noted that fungi are extremely efficient secretors of extracellular enzymes and so it might be possible to scale-up production of nanoparticles relatively easily. Aspergillus and Rhizopus species are the most common in sugar cane plantation soil and are already known to be capable of silver nanoparticle biosynthesis.

The team has identified four particular fungal strains in soil samples that can make silver nanoparticles. The products were characterised by ultraviolet-visible spectroscopy (UV-Vis), energy-dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). Regular, round particles of between 30 and 100 nanometres were obtained. These were found to be active against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, the team reports. Activity was related directly to nanoparticle concentration, the team says.

"Mycogenic synthesis of nanoparticles is a green biogenic process preferable to other alternatives," the team concludes, "Because fungi are great producers of extracellular enzymes this process makes scaling-up an easier task with high importance for clinical microbiology on the fight against microbial resistance, as well as for other industrial applications."

Related Links

AMB Express 2017, online: "Screening of filamentous fungi for antimicrobial silver nanoparticles synthesis"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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