What is Listeria?
Listeria, specifically Listeria monocytogenes, is a type of bacteria that causes a severe infection known as listeriosis. This bacterium is found in soil, dust, water, processed foods, raw meat, and animal faeces. Listeria is unique among many other germs because it can grow even in the cold temperature of the refrigerator [1].
Listeria monocytogenes is a Gram-positive, rod-shaped, non-spore-forming bacterium. It is an important foodborne bacterial pathogen for humans worldwide, with high mortality rates. It can cause a rare but severe disease called listeriosis, especially among pregnant women, the elderly, or individuals with a weakened immune system[2, 3].
Effects of a Listeria infection
Listeria infection, also known as listeriosis, can cause various symptoms and complications, depending on the individual's health status and the progression of the infection.
Listeriosis may cause fever, chills, muscle aches, nausea, and diarrhoea [4]. These symptoms might begin a few days after consuming contaminated food, but it can take up to 30 days or more for the first signs and symptoms of infection to appear [4].
If the infection spreads to the nervous system, it can lead to more severe symptoms. These include headache, stiff neck, confusion or alertness changes, balance loss, and convulsions [4].
In severe cases, listeriosis can cause necrobiotic changes in the brain and viscera and histiocytic infiltrations with the formation of granulomas. Listeria infection can also lead to life-threatening complications, including generalized blood infection and inflammation of the membranes and fluid surrounding the brain (meningitis).
Other possible complications include abscesses of the brain or liver, endocarditis, endophthalmitis, heart failure, meningoencephalitis, osteomyelitis, peritonitis, pneumonia, sepsis, and septic arthritis.
Can Listeria be killed by cooking?
Yes, Listeria can be killed with heat. Heating food to the right temperature for a specific duration effectively kills Listeria monocytogenes. For instance, cooking food to at least 70 degrees Celsius for 2 minutes significantly reduces the presence of Listeria monocytogenes [5]. This answers the common question: what temperature kills Listeria? Heating at 70°C for the appropriate time ensures that Listeria dies when cooked.
Post-package pasteurization can also be effective for fully-cooked meat products. Submerging the product in water at 96 degrees Celsius for about 10 minutes can achieve a 2- to 4-log reduction of L. monocytogenes on the surface [6]. This highlights how heating can kill Listeria, mainly when specific methods like pasteurization are applied.
A two-step cooking process—grilling followed by pasteurization—has shown a combined 4.8 log reduction in Listeria innocua M1, a nonpathogenic bacterium with slightly greater heat resistance than L. monocytogenes [7]. This provides insight into how long to cook to kill Listeria and the benefits of using combined cooking techniques to enhance safety.
It’s important to note that the effectiveness of heat in killing Listeria depends on the cooking method and duration. In a study on pork loin chops, well-done cooking in a static oven was the only treatment that completely inactivated the pathogens [8]. This confirms that proper heating procedures, such as cooking to the right temperature, are crucial to ensure Listeria is entirely eliminated.