Listeria monocytogenes is a type of bacteria that can cause a serious infection known as listeriosis. It is commonly found in soil, water, and some animals, and can contaminate food products, especially ready-to-eat meats and unpasteurized dairy products. People at higher risk for listeriosis include pregnant women, newborns, the elderly, and individuals with weakened immune systems. Symptoms may include fever, muscle aches, and gastrointestinal issues. In severe cases, it can lead to complications such as meningitis or septicemia, making it important to practice safe food handling and hygiene.