Protecting families from contaminated food and water
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Protecting families from contaminated food and water
Posted in Listeria,Our Blog on June 19, 2026
A recent study finds Listeria biofilms increase the risk of contamination in ready-to-eat foods by hiding the germ. Particularly in cold-processing environments.
The findings from scientists from the Spanish Higher Counsil for Scientific Research (CSIC) and the University of Córdoba was published in NPI Science of Food this summer.
What exactly is a biofilm? How dangerous is Listeria? Why is ready-to-eat food more vulnerable?
Follow along for the answers to these pressing questions, and more!
A biofilm is a group of microorganisms loosely working together to maintain a protective structure. Biofilms can be made up of algae, bacteria, fungi, or protozoa. They form a slimy or sticky structure that can adhere to surfaces, allowing them to persist for long periods of time.
These structures can be as much as 1000 times more resistant to pressures like antibiotics, disinfectants, and mechanical pressure.
Other research finds that Listeria monocytogenes bacteria are quite adept at making friends. In fact, within hours of being introduced, Listeria has shown to be able to colonize multispecies biofilms without disrupting the existing structure or composition and successfully persist over time.
While the matrix only allows for slow growth due to low and shared nutrient content, slow and steady wins the race.
With the advantages of biofilm, it isn’t a surprise that cross-contamination occurs. Even in environments that test regularly for these harmful germs. Even once they are discovered, it is difficult to fully remove them.
With Listeria on many peoples minds as Boar’s Head’s infamous Jarratt plant reopens amid previously exposed sanitation concerns, this research on biofilms comes at a great time.
This study on Listeria biofilms centered on a commonly contaminated product.
Ready-to-eat cold-smoked salmon.
Researchers grew both multispecies and single species biofilms from bacteria taken from around food processing environments. They grew these biofilms under low-nutrient, low-Listeria load conditions. A status likely found in real life.
They took salmon slices and touched them against those biofilms across 25 times in a row to measure potential contamination rates.
Despite potential competition for resources, multispecies Listeria biofilms seemed to be more successful. These samples showed higher growth and survival rates. Suggesting that the protective structure of coexisting microbes can positively impact Listeria bacterial proliferation.
Additionally, each successive transfer showed fewer and fewer bacterial loads. But did demonstrate the different stages of detachment.
Researchers broke this down into three stages. Initial. Unstructured. And finally, inner-layer transfer. Each layer exhibiting their own unique contamination dynamics.
One of the reasons this study was formulated was in response to 2024 amended European Commission regulation on the microbiological criteria for food. In this legislation, food business operators are tasked with ensuring that Listeria “colony forming units per gram” of a 25-gram sample not exceed 100 units throughout its shelf life.
This was put to the test.
One aspect of the study involved taking a single smoked salmon slice from an 80g package that was contaminated with Listeria from single- and multispecies biofilms. After just 15 days of refrigerated storage, the multispecies biofilm samples exceeded the regulatory limit.
This, among many other reasons, is why challenge studies should consider including multi species biofilm contamination.
Listeria monocytogenes is the bacteria responsible for the potentially deadly and life-changing illness, listeriosis.
The most common cause?
Contaminated food.
The Centers for Disease Control and Prevention (CDC) estimates that around 1,600 people become sick with listeriosis each year. About 260 deaths are associated with this illness. The agency describes it as the “third leading cause of death from foodborne illness” in the United States.
There are two categories of listeriosis. Intestinal illness and invasive illness. This unique illness affects people who are pregnant differently than those who are not. The latter experiencing more severe illness. The former experiencing unique consequences of this infection.
Intestinal illness is exactly what it sounds like. Your symptoms are fairly straightforward. People who are pregnant often experience milder symptoms, but it usually includes diarrhea and vomiting that starts within 24 hours of consuming the contaminated food and lasts between 1 and 3 days.
Intestinal illness is usually underdiagnosed because most people ride out the symptoms and illness is not serious enough to seek medical attention. Those who do get medical help for dehydration or other symptoms, may not even be diagnosed. The healthcare provider would need to order a specific test for Listeria monocytogenes to properly diagnose the infection. Unless serious or invasive, antibiotics are not administered, so knowing the specific bug is usually not all that important.
Invasive illness occurs when the bacteria spreads beyond the digestive system and enters other parts of the body. Symptoms are broken up into two categories because people who are pregnant experience different types of symptoms.
Invasive illness in pregnant people often presents as flu-like symptoms. The usual fever, muscle aches, and fatigue you would expect with the flu. Though it is not uncommon for pregnant people to show no signs of illness at all. The bigger symptoms come in the form of increased risk of miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
Invasive illness in non-pregnant people also presents flu-like symptoms, but often includes headache, stiff neck, confusion, loss of balance, and/or seizures. The mortality rate is also high. Nearly 1 in 20 non-pregnant people with invasive listeriosis will die from the infection.
Listeria contamination is not good on any food. However, ready-to-eat foods tend to be more vulnerable to Listeria biofilms.
Why?
Unlike raw food, ready-to-eat food is. Well. Ready to eat. No heat step is needed to safely consume it. Presumably, that is. It is expected to undergo whatever is necessary to render it edible.
Whether that means it is washed (as in vegetables), pasteurized (as in dairy products), or cooked (as in just about everything else).
The consumer does not need to take additional steps. So, they likely don’t.
If it is contaminated, due to no fault of their own, they may become sick.
It’s a big deal.
If you have fallen sick from eating ready-to-eat products, you may have a legal claim.
The Lange Law Firm, PLLC has helped many families with cases just like yours help hold accountable those responsible for foodborne illness. When a company becomes negligent, people become sick.
If you have become sick after eating ready-to-eat products, you should get advice. An experienced Listeria lawyer can help navigate you through the legal process.
Call (833) 330-3663 or submit your information on the online submission form for a free consultation.
By: Heather Van Tassell (contributing writer, non-lawyer)