This is an update to an overview of antimicrobials (2016), and an update (2018). It is not enough just to talk about antimicrobials; we must also address antimicrobial resistance; as it pertains to the proper use of antimicrobials and not their excessive use. But in three years’ time, there have been a number of new products, new regulations, and products that were touted as blends before and have continued down the path. There are also new findings that show that perhaps some of the biocides we use contribute to resistance (such as Methicillin-resistant Staphylococcus aureus, or MRSA) faster than others.1
The emergence and spread of antimicrobial resistance has become as a major problem. This phenomenon has elevated the alarming possibility of subsequent generations returning to the pre-antibiotic era when common infections were often fatal due to the lack of effective treatments. Medical history and research has shown that the frequency of resistant bacteria and resistant genes increase in response to the selective pressure created by the use of antibiotics.
Proof is mounting that much of the problem is rooted in the inappropriate and excessive use of antimicrobials, and that one of the most effective counter measures is to practice prudent and judicious antimicrobial usage. To achieve this societal change, we must empower health care professionals with the resources and information they need to facilitate sound decisions pertaining to antimicrobial usage.
Food contact surfaces (FCS) in food processing facilities may become contaminated with a number of unwelcome microorganisms, such as Listeria monocytogenes, Escherichia coli O157:H7, and Staphylococcus aureus. While significant efforts have been dedicated to the development of coatings that improve the antimicrobial efficacy of FCS, other important coating considerations, such as hardness, adhesion to a substrate, and migration of the antimicrobial substance into the food matrix, have largely been disregarded to the detriment of their translation into practical application. Evaluation of the current literature urges a compromise between antimicrobial effectiveness and mechanical stability in order to adhere to various regulatory frameworks as the next step toward improving the industrial feasibility of antimicrobial consumption (AMC) for FCS applications.
As a reminder of what can happen to paint when microbial action occurs, the following table outlines the scenarios.
| Property Change Due to Microbial Infection | Impact |
| Viscosity change | Polymer dispersion can become thinner or thicker depending on the effect of increased concentration of acidic byproducts. Phase separation can also occur. Viscosity increase and microbial infection can also restrict the flow within the factory equipment piping, filters, etc. |
| pH change | The metabolic by-products often are acidic in nature. The reduced pH will cause destabilization of the polymer dispersion and promote a corrosive environment both in the factory (surface of plant equipment) and once in service (corrosion of substrates). |
| Odor production | Bacteria often reduce sulfur. Other microbes have the ability to produce odors based on their biochemical reactions. |
| Gas production | Bacteria can produce hydrogen sulfide gas which leads to odor and gas production problems. |
| Color change | Microbes can change the color of the product before or after application. Sulfur-reducing bacteria generally blacken the polymer dispersion or the finished product. |
| Visible surface growth | Microbes lead to color and viscosity change (see above). |
| Corrosion | Corrosion of plant equipment and of substrates can occur from metabolic byproducts and acid production. |
| Change in properties (due mainly to reduction in molecular weight) | Breakdown of the polymer molecular weight and/or change of dispersion property characteristics can affect the end-use properties of paints and coatings. |
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Although all of these things are major, there’s been as much focus on antimicrobial resistance as there is to antimicrobial use.
More recently, the looming concern of antimicrobial resistance (AMR) has prompted the government of many countries of the world to act upon and come up with the guidelines, comprehensive recommendations and policies concerning prudent use of antibiotics and containment of AMR. However, such initiatives from countries with high incidence of antibiotic-resistant bacteria in food animals are still in infancy. The overarching aim of this evaluation is to delineate the points which need to be carried out urgently to regulate the antibiotic use in animals.
All antimicrobials refer to agents that act against microbial organisms. Microorganisms include bacteria, viruses, protozoans, and fungi such as mold and mildew.
Antimicrobials are used in protection of textiles and non-woven materials used in the manufacture of tents, sporting equipment and outdoor furniture to prevent mold and mildew and preserve wood.
They are used widely in crop protection to avoid rot and mold, Molluscicides (garden snails) as well as in preserving waterborne metalworking fluids used to lubricate cutting edges for milling steel and other metals.
In personal care, they are found in hand sanitizers, wound cleansers, dressings, etc.
The U.S. Environmental Protection Agency (EPA) regulates antimicrobial products as pesticides, and the U.S. Food and Drug Administration (FDA) regulates antimicrobial products as drugs/antiseptics. As pesticides, antimicrobial products are used on objects such as countertops, toys, grocery carts, and hospital equipment. As antiseptics, antimicrobial products are used to treat or prevent diseases on people, pets, and other living things.
If a product label claims to kill, control, repel, mitigate or reduce a pest, it is a pesticide regulated by the U.S. EPA. When manufacturers make this kind of claim on the label, they must also include:
- application instructions that are effective at killing or controlling the pest, and
- first aid instructions, in case of accidental exposure.
Specific to coatings, surfaces where an antimicrobial could be used include:
- walls and floors in hospitals and other institutions such as schools
- exterior surfaces prone to mold, algae and mildew
- ship bottoms (antifouling coatings)
- public surfaces such as handrails, light switches, etc.
Many of the antimicrobial materials used in coatings can also be employed in composites and plastics.
Due to the lengthy regulatory approval process for new antimicrobial materials, fewer and fewer new products are launched every year. However, a review of the most recent patent applications, indicates that the patents are focused on applications and less on new chemistry. Companies such as Dow Chemical continue to look at lending products in a portfolio to create new products. These blends have a greater use over the pH range in which coatings are used.
Mildew will grow on any untreated surface, as will many types of algae and mold, providing they have the correct nutrients to exist. Due to global regulatory changes, some previously-approved mildewcides as well as other antimicrobials, have been banned from use. This has caused the industry to scramble for replacements.
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This does not surprise me at all. We see cross resistance between isothiazolins and glutaraldehye as well as several other biocides in process water samples..
Challenge testing should be properly designed and include a small amount of inoculum from spoiled material. The ASTM tests with defined cultures don’t always predict how a biocide (or combination) will perform.
I agree that the ASTM test is lacking in predictability. Thank you for your comments
Overall good article on the vast subject. by summarizing almost all known.
It unfortunately gives an impression as if the subject has been stagnated at the already known.
I am not sure what you mean by stagnated at the already known. The articles are to give the reader a flavor of the topic. We don’t have the flexibility to write in depth. Hopefully, there are other Prospector articles that give you additional information, or links to other places with depth.