Listeria monocytogenes is a Gram-positive, facultatively anaerobic bacterium that causes the foodborne infection listeriosis. It has the remarkable ability to grow at refrigeration temperatures and can invade and replicate within host cells.
Biology and Pathogenicity
This small, rod-shaped bacterium is motile at temperatures below 30 °C due to peritrichous flagella that give it a characteristic tumbling motility. It is catalase-positive and can tolerate salt and a wide pH range, enabling survival in diverse environments such as soil, water, decaying vegetation, and animal feces. Listeria monocytogenes is an opportunistic pathogen that primarily affects pregnant women, newborns, older adults, and immunocompromised individuals. After ingestion of contaminated food, the bacterium uses internalins to invade intestinal epithelial cells and macrophages. Once inside, it produces listeriolysin O and phospholipases to escape the phagosome and replicate in the cytoplasm. By polymerizing host actin through the surface protein ActA, it propels itself through the cytosol and into adjacent cells, spreading without exposure to the extracellular environment. This intracellular lifestyle helps it avoid humoral immune responses and facilitates dissemination to the liver, spleen, central nervous system, and placenta. Clinical manifestations range from self-limited febrile gastroenteritis to severe outcomes such as septicemia, meningitis, and fetal loss. The bacterium’s ability to grow at refrigeration temperatures (as low as 0 °C) makes it a persistent contaminant of ready-to-eat meats, unpasteurized dairy products, and raw vegetables, necessitating strict food safety practices.
Clinical Cases and Key Facts
Significant outbreaks of listeriosis have been linked to contaminated soft cheeses, deli meats, and unpasteurized milk. For example, an outbreak associated with cantaloupes in 2011 caused numerous deaths and hospitalizations in the United States. In pregnant women, the infection may present as a mild flu -like illness yet can lead to miscarriage, stillbirth, or neonatal meningitis. Listeria monocytogenes displays a high case fatality rate compared with other foodborne pathogens, often exceeding 20 %. Routine monitoring of food processing environments and the use of pasteurization, proper refrigeration, and thorough cooking are critical control measures. Laboratory diagnosis relies on culture from blood or cerebrospinal fluid, and treatment typically involves ampicillin, sometimes combined with gentamicin.
Listeria monocytogenes is an adaptable bacterium capable of causing serious illness through contaminated food. Its ability to grow at low temperatures and move from cell to cell underscores the need for vigilance in food safety and targeted clinical care for high risk individuals.
Related Terms: Gram-Positive Bacteria, Foodborne Disease, Listeriosis, Intracellular Pathogens, Meningitis