When it comes to food safety, refrigeration is often viewed as a silver bullet for keeping harmful bacteria at bay. However, Listeria monocytogenes is a unique and dangerous exception. This resilient pathogen has evolved the ability to survive, and even thrive, at refrigeration temperatures that would typically suppress or kill most other foodborne microbes. Its cold tolerance is a key reason Listeria remains one of the deadliest foodborne pathogens in the United States and around the world.
Understanding Listeria monocytogenes
Listeria monocytogenes is a gram-positive, rod-shaped bacterium that causes listeriosis, a potentially life-threatening infection. It is particularly dangerous to pregnant women, newborns, older adults, and individuals with weakened immune systems.
According to the Centers for Disease Control and Prevention (CDC), about 1,600 cases of listeriosis occur annually in the United States, resulting in approximately 260 deaths, making Listeria one of the most lethal foodborne pathogens despite its relatively low incidence.
How Listeria Survives in the Cold
Unlike Salmonella or E. coli, Listeria can grow at temperatures as low as 0°C (32°F), which is the standard temperature for refrigeration. This trait, known as psychrotolerance, allows Listeria to persist and multiply in environments that are typically inhospitable to bacterial growth.
Cellular Adaptations
Listeria monocytogenes has developed several biological adaptations that enable its survival in cold environments:
- Membrane Fluidity: The bacterium adjusts the fatty acid composition of its cell membrane to maintain fluidity at low temperatures. This adaptation allows for normal function and nutrient transport in cold conditions.
- Cold Shock Proteins: Upon exposure to low temperatures, Listeria expresses a suite of cold shock proteins (CSPs) that help stabilize mRNA and ribosomes, ensuring continued protein synthesis and cell function.
- Compatible Solute Accumulation: The bacterium accumulates small organic molecules such as betaine and carnitine, which protect cellular structures and enzymes during stress from cold or osmotic pressure.
Implications for Food Safety
Because refrigeration does not eliminate Listeria, contaminated foods can become increasingly dangerous over time, especially if stored for prolonged periods. Common high-risk foods include:
- Ready-to-eat deli meats and hot dogs
- Unpasteurized milk and soft cheeses
- Prepackaged salads and smoked seafood
- Refrigerated pâtés or meat spreads
In industrial food production, Listeria can survive and persist in biofilms on surfaces such as slicers, conveyor belts, and drains. These biofilms are difficult to eliminate through standard cleaning and can contaminate food long after initial exposure.
Public Health Challenges
Outbreaks involving Listeria are especially concerning due to the high hospitalization and fatality rates. For example, the 2011 outbreak linked to cantaloupes from Jensen Farms caused 33 deaths and 147 illnesses, making it one of the deadliest foodborne outbreaks in recent U.S. history.
More recently, in 2025, Listeria monocytogenes was linked to Lyons ReadyCare frozen shakes, resulting in 14 deaths and 42 infections across 21 states.
These events underscore the limitations of refrigeration as a food safety measure against Listeria.
Mitigation Strategies
To protect consumers, multiple levels of intervention are necessary:
For Food Producers:
- Enhanced sanitation protocols to prevent biofilm formation
- Environmental monitoring programs to detect Listeria in processing environments
- Use of preservatives or protective cultures that inhibit bacterial growth in cold-stored products
For Consumers:
- Observe expiration dates and consume refrigerated foods promptly
- Reheat deli meats and hot dogs to steaming hot before eating
- Avoid high-risk foods if pregnant, elderly, or immunocompromised
- Clean refrigerators regularly, especially drawers and shelves where liquids may accumulate
Final Note
Listeria monocytogenes poses a unique and persistent threat to food safety due to its remarkable ability to survive and grow in cold temperatures. Unlike other pathogens that can be controlled through refrigeration, Listeria thrives in chilled environments, particularly in ready-to-eat and minimally processed foods.
This characteristic not only complicates food production and storage but also places a higher burden on public health systems during outbreaks. By understanding the science behind Listeria’s cold tolerance and implementing appropriate control measures, both industry and consumers can help reduce the risk of this potentially fatal pathogen.
