How Antibacterial Nanosilver is Becoming a Resistance Problem

By Benedette Cuffari, M.Sc.Apr 4 2017

As the most commonly used engineered nanomaterial, nanosilver has found useful applications in water and air filters, antibacterial purposes, polymer films in food packaging and much more.

The antibacterial properties of nanosilver have been successfully applied for a variety of health treatments including intravenous, urinary and tracheal catheters, endotracheal tubes, bone cements, oral cavity fillings, dietary supplements implant surgery and wound dressings.

The ability to nanosilver to prevent the spread of infection is due to release of silver (Ag⁺) ions from the surface of this material that is capable of destroying compounds that contain sulfur and phosphorus, such as the DNA and proteins present within bacteria, fungi or viruses¹.

Silver nanoparticles (AgNP) have become increasingly popular in such items due to its ability to destroy pathogens in superior potency at lower concentrations as compared to when bulk silver quantities are applied.  

While AgNP have often been employed for the aforementioned medical purposes, everyday items such as toothbrushes, toothpaste, clothing, household appliances and baby bottles have commercialized the use of nanosilver as a preventative and potent antibacterial agent².

This growing interest in the use of nanosilver and similar prophylactic antimicrobial agents is a direct result of the rapid increase in antibiotic resistance, as well as resistance to new-generation biocides, that continues to be a concern for all populations.

As one of the largest threats to global health, food security and development, antibiotic resistance is a natural process that is rapidly accelerating as a result of the misuse of antibiotics in both animals and human beings.

Infections such as tuberculosis and pneumonia are therefore becoming increasingly harder to treat as a result of this dangerous resistance, in which the mechanisms of this process are rapidly emerging and spreading throughout the world³.

The detrimental reality of antibiotic resistance is already a leading cause of increased mortality rates, higher medical costs and longer hospital stays. The use of preventative methods such as vaccinations, proper hand washing, good food hygiene practices and the use of antibacterial products, such as those containing nanosilver materials, have some promise in reducing the threat of antibiotic resistance.

While this is true, researchers are now growing concerned over the possible threat that the use of such antibacterial products, particularly those containing AgNP, can lead to its resistance as well. This threat is furthered by the rapid and widespread use of nanosilver applications, as its use has become almost a core ingredient in several different application categories.

The concept of a microorganism resistance to both silver and AgNP materials is not new. In fact, one of the earliest reports of the resistance of Salmonella typhimurium strain was documented in the 1970s, where this strain was found to contain nine resistant determinants, known as the sil genes².

Similarly, a 2013 study showed the ability of ubiquitously occurring Bacillus species bacteria to not only develop a high tolerance to AgNP, but also exhibit an enhanced proliferation following the prolonged prior exposure of the bacteria to AgNP.

In a step towards continuing this research, a team of nanobiologists led by Dr. Cindy Gunawan at the iThree Institute within the University of Technology Sydney in Australia investigated 140 commercially available medical care and dietary supplement products containing AgNP materials².

In their research, they looked at identifying the potential release of Ag⁺ following contact with body fluids, the subsequent routes of systemic Ag⁺ absorption, distribution and accumulation, and the potential exposure of microorganisms at the sites of bioavailable Ag⁺.

This study indicated that microorganisms present both inside and outside of the body have the potential to adapt to the cytotoxic ability of silver and therefore becoming resistant to it. One example of the realistic threat that nanosilver resistance could pose following chronic human consumption is shown in the presence of functional sil genes, which have been found within the gut microflora².

Aside from the silver resistance capability of these genes, the bioaccumulative potential of nanosilver following ingestion could eradicate the beneificial microflora present within the gastrointestinal tract, which could welcome pathogen growth, inflammation and disrupted energy balance, among other possible side effects.

To prevent such negative side effects from occurring, the team of researchers led by Dr. Gunawan recommend a targeted surveillance of the development of AgNP resistance is maintained in order to ensure that natural microorganism environments, such as those present within the gut microflora, do not change following exposure to AgNP materials.

Similarly, researchers recommend that the use of AgNP products be reassessed in order to determine whether the potential benefits of these applications outweigh the potential risks they pose to society.

In a concerning conclusion regarding the future health and safety of society, the team of researchers stated “Without effective regulated use of AgNP [NAg] and without efforts to monitor for potential (or realized) resistance development, the capacity of AgNP [Nag] as an alternative antimicrobial weapon in the era of increasing antibiotic resistance will be diminished. ²”

References

1. Sotiriou, Georgios A, and Sotiris E Pratsinis. “Engineering Nanosilver as an Antibacterial, Biosensor and Bioimaging Material.” Current Opinion in Chemical Engineering, Vol. 1, No. 1, 2011, pp. 3–10.
2. Cindy Gunawan et al. Widespread and Indiscriminate Nanosilver Use: Genuine Potential for Microbial Resistance, ACS Nano (2017).
3. “Antibiotic Resistance.” World Health Organization, World Health Organization, www.who.int/mediacentre/factsheets/antibiotic-resistance/en/.
4. Image Credit: shutterstock.com/KaterynaKon

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