Silver - more than a precious metal

Used for centuries, the ultimate antimicrobial is coming to lab near you

Bacteria. You can’t open a newspaper without reading about it. Whether it’s the hospital superbug MRSA (methicillin resistant Staphylococcus aureus) or Salmonella in chocolate bars, there’s no mistaking it is one of the hottest  topics around.

It’s not that there is actually more bacteria around today, it’s just that we are more aware of it than ever before. At home, our enthusiasm for fighting germs has become unstoppable and with it there has been an explosion in hygiene solutions, including antibacterial hand soaps, detergents, toothpastes and chopping boards to name but a few.

If you dig around in your kitchen cupboards you will almost certainly come up with something claiming antimicrobial protection. There are a number of antimicrobial solutions available, varying greatly in their modes of action, some have a single action others being multi functional. Many can be used as coatings, being applied after the manufacturing of a product; others can form part of the manufacturing processes as a simple addition for example in the instance of plastic mouldings.
 
There is also a variation in the ability they have in affecting the microorganism with some being Biocidal, an example of this would be a bleach or detergent giving an instant kill, others are purely biostatic and therefore maintain the levels of bacteria but do not reduce them. Anti microbial agents can be organic and therefore show the potential for less stability, or inorganic providing the added benefit of stability and prolonged effectiveness within the application.
 
Due to variations in the mode of action of the different anti microbial additives available, some bacteria (for example Pseudomonas) have the potential to develop a resistance to some of the organic additives used. With the knowledge that some strains of bacteria are either resistant or starting to show elements of resistance, what can be used as an alternative?

Possible actions of silver on microbes














Some companies are now looking to an ancient weapon in the fight against the modern ‘superbug’. People have known about silver and it’s natural antimicrobial properties for thousands of years. The ancient Phoenicians, who flourished around 1200BC, stored their water, wine and vinegar in silver bottles to prevent spoiling. Hippocrates, the father of modern medicine, noted in the 4th century BC that silver had beneficial healing and anti disease properties. The use of silver for medicinal purposes is documented from 750AD, although it wasn’t until around 1881 that the first scientific papers were published describing the medical uses of silver. Before the advent of antibiotics, during the first World War, silver compounds were used to prevent infection. Today, we see silver widely used within water filters and in water tanks, while in healthcare it is used in wound dressings and catheters.
The benefits of silver’s natural antimicrobial action have been largely exploited in applications whereby solid or colloidal silver are used. So far it hasn’t been possible to utilise this property in everyday items, such as paper, cloth or polymers. One company, however, has made ground breaking developments in incorporating silver based active ingredients into a whole range of finishes including powder coating, plastics, papers, fabrics and gel coats.

Colony counter

BioCote has been working with a wide range of manufacturers to incorporate silver into their goods which remains active for the useful life of the product. Working with approximately 40 different companies from the health, laboratory and food sectors, the portfolio of products available ranges from lockers to bench top laboratory equipment and is growing rapidly.

Biocote Marketing Executive James Sutton however is keen to point out that his customers should  not see their patented antimicrobial protection as an alternative to cleaning. “BioCote shouldn’t substitute good laboratory practice. The risk with antimicrobial products is that staff can see these as an excuse to stop normal cleaning routines, possibly creating more contamination issues than before. BioCote should be seen as an additional protection - your second line of defence”.

So how does silver reduction risk when incorporated into fomites? We all carry bacteria on our skin and act as a large vehicle capable of causing cross contamination either between hand and mouth, human to human and hand to fomites. Fomites are objects that possibly harbour a disease agent and are capable of transmitting it. Pathogens are readily transferred to hands from contaminated fomites and to the mouth from contaminated hands¹.

There are many reservoirs of transmission. These can include everyday laboratory equipment such as hot plates, stirrers and temperature measuring equipment such as thermometers, the surfaces within the laboratory itself such as the cupboards, door handles and switches, storage equipment like lockers and even large pieces of specialised equipment such as autoclaves.

The active ingredient utilised in BioCote is the element silver in the form of silver ions. It is well known that while silver is an excellent natural antimicrobial with a high efficacy against microbes, it has low toxicity against non target organisms.

The silver ions are incorporated during the material manufacturing process and are therefore present and active for the whole life of the finished product. The addition of the active ingredient does not affect the performance of the product in any other way than imparting anti-bacterial qualities.

Silver ions are slowly released from an inorganic matrix via an ion exchange mechanism. The release of silver ions is slow but fast enough to maintain an effective concentration on or near the surface of the material.

When the silver ions reach the surface of the microorganism its mechanism of antimicrobial action begins. Silver ions can bind with cell surfaces and cause disruption in cellular membrane function. However it is believed that antimicrobial activities of silver depend upon binding within the cell. Once inside the cell silver ions bind readily with electron donor groups. A prime target for silver ions is cellular thiol (-SH) groups. These are commonly found in critical proteins (enzymes).

Enzymes become denatured resulting from conformational changes caused by the binding of silver ions. Many of the enzymes denatured by silver ions are needed in the production of cellular energy. Once the energy source is removed the cell cannot maintain osmotic pressure and necessary substrates will leak out of the cell and the microbe will quickly die.

Extensive independent testing has been carried out on a wide range of bacteria including MRSA and E.coli.  Products have been tested for the simulated life of the product /material with no significant reduction in the antimicrobial performance noted, therefore demonstrating the antimicrobial efficacy for the life of the product/material.

So what does this mean for the lab? If we consider where it is most important to have a hygienic environment after hospitals and food handling we would almost always consider the laboratory. In today’s scientific laboratory we need to work accurately and fast; the enemy of this is contamination. Microbes such as bacteria and fungi, as well as putting your staff at risk, can contaminate samples distorting results and even sometimes writing-off precious samples.

A number of laboratory equipment manufacturers are working with BioCote to provide laboratory equipment with the added benefit of silver based antimicrobial protection. The likes of Comark and Priorclave have been supplying BioCote protected digital thermometers and autoclaves for 3 and 4 years respectively.

The most recent and largest company to partner BioCote is Barloworld Scientific, manufacturers of the Stuart range of bench top science equipment. Stuart offers a comprehensive range of over 100 products from colony counters to water baths, all now available with BioCote protection.

The silver based active ingredient is added into the polymer casing and control knobs with the colour, ensuring protection throughout. Metal parts are protected with BioCote modified paint and fascias are protected with BioCote treated lacquer. The addition of the active ingredients during manufacture, permanently bond them to the products ensuring they won’t rub off or leach out. Accelerated life cycle testing shows the effectiveness of BioCote treated products after 25 years, thus confirming the company’s claim that the coating will reduce cross contamination for the useful life of the product.

Rob Skehens, marketing manager of the Barloworld Scientific equipment team says: “Barloworld Scientific are very proud to launch BioCote antimicrobial protection on the Stuart range of science equipment. We always aim to provide the very best benchtop science equipment and believe that our collaboration with BioCote allows us to give our customers a much more comprehensive solution to their needs”.

There is no doubt that treated surfaces can offer an added benefit to a wide range of environments from those of a very clinical and healthcare conscious nature to ordinary domestic situations - even if it is controlling the black mould found around the bath. In between these two extremes are a wide range of other situations that can benefit from reducing the risk of cross contamination.

In most cases, manufacturers like Stuart have not increased their prices since adding BioCote to their products. At no extra cost, silver technology offers a risk reduction and creates the best possible environment for testing to be carried out in.

Silver impregnated surfaces are not a replacement for cleaning and normal procedures need to be adhered too, but it does provide an additional benefit in areas where hygiene is of a high importance. It may be time for you to think about your workplace, especially if it is a technical environment carrying out important testing. Is everything being done to assure the results are accurate? Is everything being done to protect you?