Bacteria are microscopic organisms found widely in nature, some of which can cause illness in humans. Scientific names, typically composed of two parts, provide a precise way to classify bacteria like Listeria. This standardized naming system allows for clear communication among scientists and the public regarding specific pathogens and their potential health implications.
The Scientific Name of Listeria
The full scientific name for the bacterium known to cause illness is Listeria monocytogenes. The first part of the name, Listeria, identifies the genus, which includes several species of bacteria. This genus was named in honor of Joseph Lister, a British pioneer in sterile surgery.
The second part, monocytogenes, specifies the particular species within the Listeria genus that is pathogenic to humans. This specific epithet refers to the bacterium’s ability to cause an increase in monocytes, a type of white blood cell, in the host’s bloodstream.
Listeria monocytogenes is a rod-shaped bacterium that is Gram-positive and facultatively anaerobic, meaning it can survive with or without oxygen. A notable characteristic is its ability to grow and multiply at low temperatures, even as low as 0°C (32°F), which allows it to thrive in refrigerated foods.
Sources and Transmission
Listeria monocytogenes is widely present in the environment, commonly found in soil, water, decaying vegetation, and the feces of healthy animals and humans. It can contaminate food during harvesting, processing, preparation, packing, transport, or storage.
Common food sources linked to Listeria outbreaks include ready-to-eat deli meats, unpasteurized dairy products, and soft cheeses such as Brie and Camembert. Raw produce, including sprouts and pre-cut fruits, as well as raw or smoked fish and other seafood, can also harbor the bacteria. Humans typically become infected by consuming these contaminated foods.
Listeriosis: Understanding the Infection
Listeriosis is the disease caused by infection with Listeria monocytogenes. Symptoms can vary, ranging from mild to severe, depending on the form of the illness.
Non-invasive listeriosis, often affecting otherwise healthy individuals, may present with mild symptoms like fever, muscle aches, nausea, vomiting, and diarrhea, usually lasting one to three days.
More severe, invasive listeriosis occurs when the bacteria spread beyond the intestines. This form can lead to serious conditions such as meningitis (inflammation of the brain and spinal cord membranes) or sepsis, a life-threatening response to infection. Symptoms for invasive listeriosis can include headache, stiff neck, confusion, loss of balance, and convulsions.
High-risk populations, including pregnant women, newborns, adults over 65, and individuals with weakened immune systems due to conditions like cancer or HIV/AIDS, are particularly vulnerable to severe illness and have a higher mortality rate, often between 20% and 30%.
Preventing Listeria Infection
Preventing Listeria infection involves adhering to general food safety practices. Thoroughly cooking meats, poultry, and seafood to their safe internal temperatures helps eliminate the bacteria. Avoid cross-contamination by using separate cutting boards and utensils for raw and ready-to-eat foods, and wash hands with soap and warm water for at least 20 seconds before and after handling food.
Proper refrigeration temperatures are important; refrigerators should be kept at or below 40°F (4°C) to slow bacterial growth. Ready-to-eat foods, such as deli items and leftovers, should be consumed promptly and not stored for longer than seven days. Regularly cleaning the refrigerator, including wiping up spills immediately and cleaning interior surfaces with hot water and mild detergent, helps prevent Listeria from growing and spreading.
High-risk individuals should take additional precautions. They should avoid unpasteurized milk and products made from it, such as certain soft cheeses. Deli meats and hot dogs should be reheated until steaming hot before consumption, and refrigerated smoked seafood should be avoided unless it is canned, shelf-stable, or fully cooked. Raw sprouts should also be avoided by these groups.