The History and Benefits of Antimicrobial Coatings

illustration of microscopic fungi growth

By Cynthia A. Gosselin, The ChemQuest Group

The desire for protection from molds, viruses, bacteria—indeed, microbes of all kinds—did not begin with the onset of the current COVID-19 pandemic.

In 800 BC, Homer’s epic poems, Iliad and Odyssey, contained references to using sulfur to control fungal disease. Ancient Egyptian embalmers used cinnamon-infused bandages to control mold. Notably, Spanish researchers recently infused wax-paper bread wrapping with cinnamon that reduced mold by 96%, prolonging freshness by 10 days.

More than 3,000 years ago, the Bible recorded mold as an indoor environmental health concern that caused “leprosy”—a comprehensive term used to describe infectious skin diseases related to spore-producing bacteria or mold. Mold was considered such a serious health hazard that residents were ordered to leave their homes until remediation could be performed by the high priest. If that didn’t work, homes were burned.

Medieval societies used a broad range of natural substances as remedies for Staphylococcus aureus, a bacteria that can cause staph infections and other diseases. A team from the University of Nottingham reproduced a cocktail from a 10th century Anglo-Saxon leech book and found that it repeatedly killed S. aureus biofilms in vitro mode, soft-tissue infection as well as methicillin-resistant S. aureus (MRSA) in a mouse chronic-wound model.1

Seed-protectant fungicides were developed in 1767 when copper sulfate was used to control bunt in grains. Lime sulfur was developed in 1802 to control powdery mildew on fruit trees.2

Metals have also been used for more than 3,000 years as protection from a variety of microbes. Ancient Greeks and Egyptians used silver vessels to keep water and other liquids fresh. In the Middle Ages, the wealthy stored and ate their food from silver containers to keep bacteria from growing. It is also believed that silverware protected the wealthy from the worst of the plague.

Copper is also an ancient remedy against many pathogens. Ancient Egyptians used copper to sterilize drinking water and cure headaches and skin conditions. The Aztecs gargled with a copper infused solution to cure sore throats. In 1882, Pierre-Marie-Alexis Millardet, a Frenchman, discovered that grapevines that had been sprayed with a mixture of lime and copper sulfate were free of down mildew. This led to the classic 3:1:100 mixture ratio of copper sulfate to calcium oxide to water that is still used today.

Applying Science to Antimicrobial Coatings

Fast forward to 2021, and many of the ancient problems of food storage and preservation and disease mitigation have been solved. However, many of the same concerns around infectious properties of harmful bacteria, mold, fungi, and other microbes are still of great concern. Mold and mildew can cause millions of dollars in damage to homes and office buildings. Superbugs that are resistant to antibiotics are becoming serious issues in hospitals.

Dr. Chuck Gerba, professor of environmental microbiology at the University of Arizona, has long studied novel solutions to these problems. According to Gerba, the “next generation of hygiene” will come from continuously acting antimicrobial surfaces that are protective coatings infused with microbe resistant quaternary ammonium salts, copper, or silver.

Gerba highlighted a study where a virus tracer was seeded on a doorknob in an office with 100 employees.3 Within four hours, half the office space and half the employees were “infected” with the tracer. The study determined that viruses and other microbes move around very efficiently. If an antimicrobial coating had been applied to that “ground zero infected doorknob,” the virus would have been denatured and rendered unable to infect either the rest of the office or the staff.

Antimicrobial coatings contain ingredients (such as silver, copper, or quaternary ammonium salts) that destroy the membranes or enzymes surrounding the molecule and produce oxidizers that ultimately destroy the protein structure—rendering the microbe incapable of causing harm.

One of the major advantages of antimicrobial coatings is that they disinfect continuously if the coating remains intact on the surface. Although this will not eliminate the need for manual cleaning and disinfecting, the coating provides an additional level of protection in-between hygiene protocols.

For example, airborne viruses attach to floors in hospitals. Simply walking on the floors can re-aerosolize the virus and it becomes airborne to infect again as staff move from room to room. Floors painted with antimicrobial coatings would denature the virus, thereby inhibiting the microbe from becoming virulently airborne.

Antimicrobial wall paint has been shown to protect against odor and stain-causing bacteria. Several paints have been shown effective in killing 99% of S. aureus, E. coli, vancomycin-resistant enterococcus (VRE), and MRSA.4 Some brands are found to be effective for four years as long as film integrity is maintained. Coatings containing polymeric silanated quaternaries have been shown to be effective against bacteria and mold for at least 90 days. These sanitizing latex paints are available to the general public from any paint or big-box store.

A pre-painted, silver-containing coating has been shown to be effective in greatly reducing mold, fungi, and bacteria after 10 years of continuous service in homes and hospitals.5 Today, those pre-painted coatings are available for heating and air conditioning systems, commercial refrigeration systems, appliances, and building components. These antimicrobial coatings continually suppress the growth of microbes on the surfaces of these components, keeping them cleaner and more sanitary. The controlled release of silver ions provides continuous protection by inhibiting the growth of bacteria, mold, mildew, fungi, and other microbes, even at refrigeration temperatures.

These modern-day continuously acting antimicrobial coatings could have a huge immediate impact on health and safety by decreasing the transmission of viruses, bacteria, and mold in-between manual cleaning/disinfecting protocols. One problem with implementing these products is that the U.S. Environmental Protection Agency does not yet have a standard testing protocol for these novel continuously acting products. Modernizing the testing process to incorporate these properties in a way that would provide confidence in the longevity of the antimicrobial action would be extremely helpful. To date, microbes have not shown a resistance to these antibacterial ingredients—so modernizing the testing process a worthy investment. Because some bacteria are becoming antibiotic resistant, the ability of a coating to eliminate the microbe before it infects a human host would be a giant step in the right direction for developing, as Gerba says, “the next generation of hygiene.”

 

References

  1. Lee, Christina. “AncientBiotics—A Medieval Remedy for Modern Day Superbugs?” University of Nottingham. March 2015 press release.
  2. Morton, V., and Staub, T. A Short History of Fungicides. Online. APSnet Features. 2008. DOI: 10.1094/APSnetFeature-2008-0308 (accessed Sept 21, 2021).
  3. Private Communication with Dr. Charles Gerba, Professor of Environmental Microbiology. University of Arizona. September 2021.
  4. Sherwin-Williams Company. “Keep Walls Sanitized 42/7 with SuperPaint® with Sanitizing Technology.” 2021.
  5. Maxwell, Sheri, and Gerba, Charles P. “Evaluation of Surfaces at the Concept Home After Ten Years of Service.” Department of Soil, Water, and Environmental Science, University of Arizona. June 11, 2014.
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