Listeria monocytogenes

Listeria monocytogenes

Listeria monocytogenes under a microscope.

Listeria monocytogenes is a Gram-positive bacterium, known for causing the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in both oxygen-rich and oxygen-poor environments. This bacterium is of significant concern in the food industry due to its ability to grow at low temperatures, such as those found in refrigerated foods.

Characteristics

Listeria monocytogenes is a rod-shaped bacterium that is motile at room temperature due to the presence of flagella. It is non-spore-forming and can grow in a wide range of temperatures, from 1°C to 45°C. This adaptability allows it to thrive in various environments, including soil, water, and decaying vegetation.

Pathogenesis

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Life cycle of Listeria monocytogenes.

Listeria monocytogenes is an intracellular pathogen, meaning it can invade and live within the cells of its host. The bacterium enters the host through the gastrointestinal tract, often via contaminated food. Once inside the host, it can spread to the liver, spleen, and central nervous system, leading to severe infections such as meningitis and encephalitis.

The bacterium's ability to move within and between cells is facilitated by the actin-based motility mechanism, where it hijacks the host cell's actin to propel itself.

Clinical Manifestations

Listeriosis primarily affects pregnant women, newborns, the elderly, and individuals with weakened immune systems. In pregnant women, the infection can lead to miscarriage, stillbirth, or severe illness in the newborn. In other populations, it can cause symptoms ranging from mild flu-like symptoms to severe infections such as septicemia and meningitis.

Diagnosis and Treatment

Listeria monocytogenes grown on selective agar.

Diagnosis of listeriosis is typically confirmed through the isolation of Listeria monocytogenes from a normally sterile site, such as blood or cerebrospinal fluid. Culturing the bacterium on selective media, such as Listeria selective agar, aids in its identification.

Treatment involves the use of antibiotics, with ampicillin and gentamicin being the most commonly used. Early diagnosis and treatment are crucial to prevent severe outcomes.

Prevention

Preventing listeriosis involves proper food handling and preparation practices. This includes thoroughly cooking food, avoiding unpasteurized dairy products, and maintaining good hygiene in food processing environments.

Related Pages

• Listeriosis
• Gram-positive bacteria
• Foodborne illness