Mitigating Listeria Risks with Dursan Coating

Recent headlines have highlighted a tragic Listeria outbreak linked to deli meats, that resulted in nine deaths. This incident brings attention to the persistent threat of Listeria in food production. However, SilcoTek coatings could help mitigate such risks. Dursan^®-coated stainless steel surfaces have been shown to significantly reduce Listeria biofilm formation. By utilizing our coatings in food processing environments, especially where deli meats are handled, the industry could take a major step toward preventing future outbreaks and enhancing food safety.

We will demonstrate how Dursan reduces protein binding, corrosion, and biofilm formation on surfaces, making it a potential game-changer in protecting consumers against foodborne illnesses. This is particularly crucial in the context of deli meats, which have been identified as a common source of Listeria contamination.

What is Listeria? 

As defined by the Food and Drug Administration (FDA), "Listeria monocytogenes (L. monocytogenes) is a species of pathogenic (disease-causing) bacteria that can be found in moist environments, soil, water, decaying vegetation and animals, and can survive and even grow under refrigeration and other food preservation measures. When people eat food contaminated with L. monocytogenes, they may develop a disease called listeriosis. L. monocytogenes is generally transmitted when food is harvested, processed, prepared, packed, transported or stored in environments contaminated with L. monocytogenes. Environments can be contaminated by raw materials, water, soil, and incoming air. Pets can also spread the bacteria in the home environment if they eat food contaminated with L. monocytogenes." 

What does it do humans? 

Listeria infection, also known as Listeriosis, can cause very mild to severe, life-threatening symptoms. Because it is transmitted to food products, it is particularly dangerous to those who are at higher risk of becoming sick, like pregnant women, newborns, those over 65 years old, and those who have weakened immune systems. Unborn babies are especially at risk of preterm labor, stillbirth, miscarriage, neonatal meningitis, or sepsis. Maternal listeriosis carries a mortality rate of 20-30% in unborn babies. 

Common symptoms of Listeriosis are: 

• Fever 
• Chills 
• Muscle aches 
• Nausea 
• Diarrhea 

More serious symptoms include: 

• Headache 
• Stiff neck 
• Confusion or changes in alertness 
• Loss of balance 
• Convulsions 

If you experience any of these symptoms after eating or drinking anything that could have come into contact with Listeria, please seek medical attention. 

Heating meats to a temperature above 165° will kill Listeria, which can survive refridgeration and freezing. For more information about Listeria, check out the CDC's website. 

Listeria Formation

Listeria bacteria naturally occurs in soil, water, and animal feces. When dairy products, raw fruits and vegetables are processed and packaged, the listeria bacteria can transfer to the equipment and form biofilms. Once these biofilms are formed, they are difficult to remove and often require shutting down the process for extensive cleaning. Without complete equipment cleaning, the listeria can transfer to previously unaffected produce or products, causing food contamination and a major listeria outbreak. A major outbreak can result in hundreds of sick people and extensive product recalls. 

How do SilcoTek coatings help? 

Dursan coatings are effective even on textured surfaces, which are typically harder to clean. Food producers could benefit from incorporating Dursan-coated equipment, particularly in high-risk areas like meat and dairy processing. By reducing biofilm formation, these surfaces not only enhance food safety but also simplify cleaning processes, ultimately protecting consumers from potential Listeria outbreaks.

Dursan is an NSF certified and FDA compliant coating process that improves the inertness, durability, anti-fouling, and corrosion resistant properties of substrates in a variety of industries. 

The Department of Biomedical and Nutritional Sciences at the University of Massachusetts, Lowell and the Agricultural Research Service at the United States Department of Agriculture researched how different coatings can reduce listeria biofilm formation on stainless steel. The researchers looked at 304 stainless steel with different surface textures and FDA approved coatings. As shown below, Dursan performed very well in comparison to the other coatings, especially on the native 304 surface. 

304 stainless steel is the most widely used material for food processing equipment due to its relatively high corrosion resistance, its durability, and low cost compared to specialty steel alloys. Here, the researchers investigated five different coatings as seen in Table 1. According to the paper, all 5 of the coatings are FDA approved coatings; however, it is important to remember that components and systems must go through the FDA approval process on their own, not the coating. All 5 of these coatings are FDA and USDA compliant, meaning that they can pass any FDA approvals that may be necessary to bring a product to market.

In addition to the coatings, the authors explored altering the topography of the stainless steel samples. Surface roughness can be present in a variety of size domains. For instance, some glasses can be made atomically smooth, meaning the surface roughness is on the size order of picometers. Other roughness domains can be on the order of millimeters such as Velcro or corduroy fabric. Each roughness domain can potentially have a different impact on the ability for a bacteria or other organism to “stick” to the surface. In the paper, the researchers investigated and compared several surfaces including:

• A relatively smooth, machine finished surface.
• A slightly rougher, brushed surface.
• A micropatterned, pillar surface.

The various surfaces were coated and compared. The various coatings compared are shown below.

Table 1: List of the 5 coatings the researchers investigated in writing this paper.

Data

The biofilm formation was quantified in two different ways: CV staining and plate counts. According to the authors, CV staining is a method that can quantify the total biomass on the surface. This includes the bacterial cells (the listeria) as well as the extracellular polymeric substances. What it cannot quantify is cell populations or any individual extracellular polymeric substance. The plate count experiment was used to quantify viable bacterial colonies. In other words, the CV staining shows the total mass of biological substance that was on the sample surface while the plate counts show how much of that substance is viable cells that can make a person sick.

The CV staining results show that only 3 coatings provide statistically lower biomass accumulation: Dursan, Ni-P-PTFE, and CrN. 

CV staining results of all 18 samples. 

The symbols over the coated samples symbolize statistical difference (P-values) for each result. **: P<0.001 or significantly different from the uncoated control, *: 0.001<P<0.05 or statistically different from the control, and ∇: P>0.05 or not statistically different from the control. 

One interesting note is the dramatic increase in biomass accumulation on the ceramic coated surfaces for the brushed coating (304-4). According to the authors, this result was not surprising for the TiN because it was previously reported that TiN encourages biofilm formation. It is unclear as to why the coatings only encourage adhesion on the brushed surface.

The results of the viable cell counts from each surface showed that, regardless of the surface topography, Dursan is the only coating that is able to decrease active cells from the surface. Results showed up to roughly a 4X reduction in viable cell count. 

Measurement of active listeria cells on the surface of various coupons.

The indicators over the bars are the same as they were for Figure 2 where ** shows a significant statistical difference from the control, * shows statistical difference, and ∇ shows essentially no statistical difference.

The relatively small decrease on the brushed 304 stainless surface (304-4) is not well explained in the paper. It could be that the surface roughness is of the correct order of magnitude to encourage bacterial adhesion, but then disrupt the biofilm formation, this anomaly needs further exploration.

Texturing of surfaces as well as protective coatings have previously been explored to mitigate listeria contamination, but the combination of the two have not been extensively studied.

Learn more about coatings for bio inertness and medical diagnostics on our Life Sciences page.

Conclusion

Dursan is a low surface energy, inert coating designed to reduce nonspecific protein binding and carryover while improving corrosion resistance. Food production and diagnostic equipment used for protein analysis will benefit from the durability and chemical inertness of Dursan coated stainless steel and glass. SilcoTek provides an alternative coating solution in Dursan that offers better stability in air and other oxidative environments, even under elevated temperatures.

By adopting advanced surface treatments like Dursan, food producers can create cleaner, safer environments, ultimately protecting consumers from dangerous pathogens. This proactive approach could save lives and prevent the kind of tragedies currently making headlines.

Have a question about your application? Want to know more about Dursan's benefits? Contact our coating experts! 

References: 

Centers for Disease Control and Prevention. (2024, August 28). Investigation update: Listeria outbreak, meats sliced at Delis. Centers for Disease Control and Prevention. https://www.cdc.gov/listeria/outbreaks/details-delimeats-7-24.html. 

Rovas, L., Razbadauskas, A., & Slauzgalvyte, G. (2023, May 6). Listeriosis during pregnancy: Maternal and neonatal consequences-A case report. International journal of women’s health. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10171218/.