Listeria

Listeria is a genus of Gram-positive, non-spore-forming bacteria. The species most important to human health is Listeria monocytogenes, which causes listeriosis, a disease that ranges from mild flu-like illness to invasive infection of the bloodstream and central nervous system. L. monocytogenes is a facultative intracellular pathogen that can grow within cells and at refrigeration temperatures, a feature that contributes to its persistence in food and environments.

Key laboratory and biological traits include small, motile rods that are catalase-positive and can exhibit tumbling motility at room temperature. It can be detected in blood, cerebrospinal fluid, amniotic fluid, and other sterile sites, and it may be identified by culture or molecular methods.

Transmission typically occurs via ingestion of contaminated food. Common sources include unpasteurized dairy products, soft cheeses, deli meats, smoked seafood, and other ready-to-eat foods. The bacterium can cross the intestinal barrier and, in pregnant people, cross the placenta, potentially causing fetal infection, miscarriage, or neonatal illness. Adults who are healthy often experience mild gastroenteritis; invasive disease is more likely in pregnant people, newborns, older adults, and those with weakened immune systems.

Clinical presentation depends on the form of disease. Febrile gastroenteritis is common in healthy individuals; invasive listeriosis can cause meningitis, encephalitis, or bacteremia. Incubation for invasive disease is typically one to several weeks.

Diagnosis relies on culture or PCR from blood, CSF, or other clinical specimens. Treatment usually involves antibiotics such as ampicillin, often with gentamicin; alternatives exist for penicillin-allergic patients or specific settings. Prevention emphasizes food safety, including pasteurization, proper cooking, refrigeration, and avoidance of high-risk foods for vulnerable populations. Public health measures address outbreaks linked to contaminated foods.