Tag Archives: colloidal silver

Is there a risk of resistance to nanosilver?

Anyone who’s noticed how popular silver has become as an antibacterial, antifungal, or antiviral agent may have wondered if resistance might occur as its use becomes more common. I have two bits on the topic, one from Australia and the other from Canada.


Researchers in Australia don’t have a definitive statement on the issue but are suggesting more caution (from a March 31, 2017 news item on Nanowerk),

Researchers at the University of Technology Sydney [UTS] warn that the broad-spectrum antimicrobial effectiveness of silver is being put at risk by the widespread and inappropriate expansion of nanosilver use in medical and consumer goods.

As well as their use in medical items such as wound dressings and catheters, silver nanoparticles are becoming ubiquitous in everyday items, including toothbrushes and toothpaste, baby bottles and teats, bedding, clothing and household appliances, because of their antibacterial potency and the incorrect assumption that ordinary items should be kept “clean” of microbes.

Nanobiologist Dr Cindy Gunawan, from the ithree institute at UTS and lead researcher on the investigation, said alarm bells should be ringing at the commercialisation of nanosilver use because of a “real threat” that resistance to nanosilver will develop and spread through microorganisms in the human body and the environment.

A March 31 (?), 2017 University of Technology Sydney press release by Fiona McGill, which originated the news item, expands on the theme,

Dr Gunawan and ithree institute director Professor Liz Harry, in collaboration with researchers at UNSW [University of New South Wales] and abroad, investigated more than 140 commercially available medical devices, including wound dressings and tracheal and urinary catheters, and dietary supplements, which are promoted as immunity boosters and consumed by throat or nasal spray.

Their perspective article in the journal ACS Nano concluded that the use of nanosilver in these items could lead to prolonged exposure to bioactive silver in the human body. Such exposure creates the conditions for microbial resistance to develop.

E. coli bacteria. Photo: Flickr/NIAID


The use of silver as an antimicrobial agent dates back centuries. Its ability to destroy pathogens while seemingly having low toxicity on human cells has seen it widely employed, in treating burns or purifying water, for example. More recently, ultra-small (less than 10,000th of a millimetre) silver nanoparticles have been engineered for antimicrobial purposes.  Their commercial appeal lies in superior potency at lower concentrations than “bulk” silver.

“Nanosilver is a proven antimicrobial agent whose reliability is being jeopardised by the commercialisation of people’s fear of bacteria,” Dr Gunawan said.

“Our use of it needs to be far more judicious, in the same way we need to approach antibiotic usage. Nanosilver is a useful tool but we need to be careful, use it wisely and only when the benefit outweighs the risk.

“People need to be made aware of just how widely it is used, but more importantly they need to be made aware that the presence of nanosilver has been shown to cause antimicrobial resistance.”

What is also needed, Dr Gunawan said, is a targeted surveillance strategy to monitor for any occurrence of resistance.

Professor Harry said the findings were a significant contribution to addressing the global antimicrobial resistance crisis.

“This research emphasises the threat posed to our health and that of the environment by the inappropriate use of nanosilver as an antibacterial, particularly in ordinary household and consumer items,” she said.

Here’s a link to and a citation for the paper,

Widespread and Indiscriminate Nanosilver Use: Genuine Potential for Microbial Resistance by Cindy Gunawan, Christopher P. Marquis, Rose Amal, Georgios A. Sotiriou, Scott A. Rice⊥, and Elizabeth J. Harry. ACS Nano, Article ASAP DOI: 10.1021/acsnano.7b01166 Publication Date (Web): March 24, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Meanwhile, researchers at the University Calgary (Alberta, Canada) may have discovered what could cause resistance to silver.


This April 25, 2017 news release on EurekAlert is from the Experimental Biology Annual Meeting 2017,

Silver and other metals have been used to fight infections since ancient times. Today, researchers are using sophisticated techniques such as the gene-editing platform Crispr-Cas9 to take a closer look at precisely how silver poisons pathogenic microbes–and when it fails. The work is yielding new insights on how to create effective antimicrobials and avoid the pitfalls of antimicrobial resistance.

Joe Lemire, a postdoctoral fellow at the University of Calgary, will present his work in this area at the American Society for Biochemistry and Molecular Biology annual meeting during the Experimental Biology 2017 meeting, to be held April 22-26 in Chicago.

“Our overarching goal is to deliver the relevant scientific evidence that would aid policymakers in developing guidelines for when and how silver could be used in the clinic to combat and control infectious pathogens,” said Lemire. “With our enhanced mechanistic understanding of silver toxicity, we also aim to develop novel silver-based antimicrobial therapies, and potentially rejuvenate other antibiotic therapies that bacteria have come to resist, via silver-based co-treatment strategies.”

Lemire and his colleagues are using Crispr-Cas9 genome editing to screen for and delete genes that allow certain bacterial species to resist silver’s antimicrobial properties. [emphasis mine] Although previous methods allowed researchers to identify genes that confer antibiotic resistance or tolerance, Crispr-Cas9 is the first technology to allow researchers to cleanly delete these genes from the genome without leaving behind any biochemical markers or “scars.”

The team has discovered many biological pathways involved in silver toxicity and some surprising ways that bacteria avoid succumbing to silver poisoning, Lemire said. While silver is used to control bacteria in many clinical settings and has been incorporated into hundreds of commercial products, gaining a more complete understanding of silver’s antimicrobial properties is necessary if we are to make the most of this ancient remedy for years to come.


Joe Lemire will present this research at 12-2:30 p.m. Tuesday, April 25, [2017] in Hall F, McCormick Place Convention Center (poster B379 939.2) (abstract). Contact the media team for more information or to obtain a free press pass to attend the meeting.

About Experimental Biology 2017

Experimental Biology is an annual meeting comprised of more than 14,000 scientists and exhibitors from six host societies and multiple guest societies. With a mission to share the newest scientific concepts and research findings shaping clinical advances, the meeting offers an unparalleled opportunity for exchange among scientists from across the U.S. and the world who represent dozens of scientific areas, from laboratory to translational to clinical research. http://www.experimentalbiology.org #expbio

About the American Society for Biochemistry and Molecular Biology (ASBMB)

ASBMB is a nonprofit scientific and educational organization with more than 12,000 members worldwide. Founded in 1906 to advance the science of biochemistry and molecular biology, the society publishes three peer-reviewed journals, advocates for funding of basic research and education, supports science education at all levels, and promotes the diversity of individuals entering the scientific workforce. http://www.asbmb.org

Lemire’s co-authors for the work presented at the 2017 annual meeting are: Kate Chatfield-Reed (The University of Calgary), Lindsay Kalan (Perelman School of Medicine), Natalie Gugala (The University of Calgary), Connor Westersund (The University of Calgary), Henrik Almblad (The University of Calgary), Gordon Chua (The University of Calgary), Raymond Turner (The University of Calgary).

For anyone who wants to pursue this research a little further, the most recent paper I can find is this one from 2015,

Silver oxynitrate: An Unexplored Silver Compound with Antimicrobial and Antibiofilm Activity by Joe A. Lemire, Lindsay Kalan, Alexandru Bradu, and Raymond J. Turner. Antimicrobial Agents and Chemotherapy 05177-14, doi: 10.1128/AAC.05177-14 Accepted manuscript posted online 27 April 2015

This paper appears to be open access.

Carbohydrates could regulate the toxicity of silver nanoparticles

According to a Jan. 22, 2015 news item on Azonano, you can vary the toxic impact of silver nanoparticles on cells by coating them with carbohydrates,

The use of colloidal silver to treat illnesses has become more popular in recent years, but its ingestion, prohibited in countries like the US, can be harmful to health. Scientists from the Max Planck Institute in Germany have now confirmed that silver nanoparticles are significantly toxic when they penetrate cells, although the number of toxic radicals they generate can vary by coating them with carbohydrates.

A Jan. 21, 2015 Spanish Foundation for the Science and Technology (FECYT) news release on EurekAlert, which originated the news item, describes colloidal silver and its controversies and the research on limiting silver nanoparticle toxicity to cells,

Silver salts have been used externally for centuries for their antiseptic properties in the treatment of pains and as a surface disinfectant for materials. There are currently people who use silver nanoparticles to make homemade potions to combat infections and illnesses such as cancer and AIDS, although in some cases the only thing they achieve is argyria or blue-tinged skin.

Health authorities warn that there is no scientific evidence that supports the therapeutic efficiency of colloidal silver and in fact, in some countries like the US, its ingestion is prohibited. On the contrary, there are numerous studies which demonstrate the toxicity of silver nanoparticles on cells.

One of these studies has just been published in the ‘Journal of Nanobiotechnology‘ by an international team of researchers coordinated from the Max Planck Institute of Colloids and Interfaces (Germany). “We have observed that it is only when silver nanoparticles enter inside the cells that they produce serious harm, and that their toxicity is basically due to the oxidative stress they create,” explains the Spanish chemist Guillermo Orts-Gil, project co-ordinator, to SINC.

To carry out the study, the team has analysed how different carbohydrates act on the surface of silver nanoparticles (Ag-NP) of around 50 nanometres, which have been introduced into cultures of liver cells and tumour cells from the nervous system of mice. The results reveal that, for example, the toxic effects of the Ag-NP are much greater if they are covered with glucose instead of galactose or mannose.

‘Trojan horse’ mechanism

Although not all the details on the complex toxicological mechanisms are known, it is known that the nanoparticles use a ‘Trojan horse’ mechanism to trick the membrane’s defences and get inside the cell. “The new data shows how the different carbohydrate coatings regulate the way in which they do this, and this is hugely interesting for controlling their toxicity and designing future trials,” points out Orts-Gil.

The researcher highlights that there is a “clear correlation between the coating of the nanoparticles, the oxidative stress and toxicity, and thus, these results open up new perspectives on regulating the bioactivity of the Ag-NP through the use of carbohydrates”.

Silver nanoparticles are not only used to make homemade remedies; they are also increasingly used in drugs such as vaccines, as well as products such as clothes and cleaning cloths.

Here’s a link to and a citation for the paper,

Carbohydrate functionalization of silver nanoparticles modulates cytotoxicity and cellular uptake by David C Kennedy, Guillermo Orts-Gil, Chian-Hui Lai, Larissa Müller, Andrea Haase, Andreas Luch, and Peter H Seeberger. Journal of Nanobiotechnology 2014, 12:59 doi:10.1186/s12951-014-0059-z published 19 December 2014

This is an open access paper. One final observation, David Kennedy, the lead author, is associated with both the Max Planck Institute and the Canada National Research Council and, depending on which news release (SINC news site Jan. 20, 2015) you read, Guillermo Orts-Gil is identified as a Spanish chemist and coordinator for SINC (Science News and Information Service).

Surprising facts about silver nanoparticles from the University of Michigan

Dr. Andrew Maynard, Director of the University of Michigan’s Risk Science Center, has featured seven surprising facts about silver nanoparticles in his latest video in the Risk Bites series. Before getting to the video,here’s an introduction to the topic of silver nanoparticles from a Feb. 18, 2014 posting by Ishani Hewage on the University of Michigan’s Risk Sense blog (Note: A link has been removed),

Silver – known for its germ-killing capabilities – has been used for thousands of years. In recent times though, concerns have been raised over the potential health and environmental risks associated with one particular form of silver that has been used increasingly in a range of products: engineered silver nanoparticle. In this week’s Risk Bites, Andrew Maynard, director of the Risk Science Center, rounds-up seven aspects of silver nanoparticles that might help you weigh up their risks and benefits.

“Silver has long been used for its medicinal properties,” says Andrew. “People used to intentionally dose themselves with silver nanoparticles in the form a silver laced tonic as a cure-all.”

Nowadays, the use of silver nanoparticles is not just limited to the medical field. The military, athletes and manufactures are increasingly using them to develop smart new technologies that inhibit bacterial growth and enhance overall performance.  These microscopically small particles make it easier to get silver into products without compromising them …

Without more ado, here’s the video, ‘7 surprising facts about silver nanoparticles and health’:

Both the blog posting and this link will lead you to more information about silver nanoparticles.

Nanosilver history

According to Empa researchers, Bernd Nowack and Harald Krug, together with Murray Heights of the company HeiQ, silver at the nanoscale has a long history. From the Jan. 31,2011 news item on physorg.com,

Nanosilver is not a new discovery by nanotechnologists — it has been used in various products for over a hundred years, as is shown by a new Empa study. The antimicrobial effects of minute silver particles, which were then known as “colloidal silver,” were known from the earliest days of its use.

Their paper showing that nanosilver is not a 21st century discovery is being published in Environmental Science & Technology. From the news item,

Silver particles with diameters of seven to nine nm were mentioned as early as 1889. They were used in medications or as biocides to prevent the growth of bacteria on surfaces, for example in antibacterial water filters or in algaecides for swimming pools.

The nanoparticles were known as “colloidal silver” in those days, but what was meant was the same then as now – extremely small particles of silver. The only new aspect is the use today of the prefix “nano”. “However,” according to Bernd Nowack, “nano does not mean something new, and nor does it mean something that is harmful.” When “colloidal silver” became available on the market in large quantities in the 1920s it was the topic of numerous studies and subject to appropriate regulation by the authorities. [emphasis mine]

This suggests that there has been sufficient research on what we now call nano silver and its impact on the environment and on health. By contrast, the California Department of Toxic Substances Control (DTSC) had this to say in its recent call for information about analytical test methods for nanomaterials (from the Dec. 27, 2010 news item on Nanowerk),

Nano Silver

Nano silver is used increasingly in many consumer products. These include food contact materials (storage containers, cups, bowls and cutting boards), children’s toys and infant products, disinfectants, cosmetics, cleaning agents and machines, textiles, athletic apparel, dyes/paints, varnishes, polymers, and in medical products and applications. Given these diverse applications, nano silver is likely entering the environment. Several scientific studies describe potential adverse effects of nano silver on publicly owned treatment works (wastewater collection, treatment, and disposal systems).

Silver has been known historically as a potent antibacterial, antifungal, and antiviral agent. In recent years, silver is used as a biocide in solution, suspension, and in nano-particulate form. The strong antimicrobial activity is a major reason for the development of products that contain nano silver. Nano silver may also have applications in agricultural, vector, and urban pest control. However, little or no information about detecting and measuring the effect of nano silver in the environment exists. Recent published papers point out difficulties in quantifying the existence of nano particles in environmental and biological contexts, which presents challenges in estimating and assessing the hazards and risks of nano silver. [emphasis mine]

Nowack, one of the Empa researchers, provides evidence for his position in a commentary that was previously published in the journal Science (from the news item),

A commentary by Bernd Nowack in the scientific journal Science discusses the implications of the newest studies on nanosilver in sewage treatment plants. More than 90% remains bound in the sewage sludge in the form of silver sulfide, a substance which is extremely insoluble and orders of magnitude less poisonous than free silver ions. [emphasis mine] It apparently does not matter what the original form of the silver in the wastewater was, whether as metallic nanoparticles, as silver ions in solution or as precipitated insoluble silver salts.

“As far as the environmental effects are concerned, it seems that nanosilver in consumer goods is no different than other forms of silver and represents only a minor problem for eco-systems,” says Nowack. What is still to be clarified, however, is in what form the unbound silver is present in the treated water released from sewage works, and what happens to the silver sulfide in natural waters. Is this stable and unreactive or is it transformed into other forms of silver? [emphasis mine]

The two approaches are not directly contradictory but I do find the totality confusing. Which challenges about the hazards and risks of nano silver are the folks in California referring to? It seems they’re not familiar with the older research cited by Nowack or perhaps they know something Nowack and his colleagues do not. Meanwhile, Nowack’s Science commentary is reassuring but whoever wrote the news item was careful to point out that there is still some important work to be done before declaring nano silver to be a ‘safe’ substance.

I posted about the DTSC call for information, Feb. 7, 2011.