Listeria Monocytogenes (Listeriosis)

Causes febrile gastroenteritis and meningitis. Ubiquitous in the environment - resides in animals, plants, and soil. Also grows readily in cold temperatures. In the U.S., infectious outbreaks are associated with contaminated unpasteurized dairy products and deli meats. Short rods; some authors categorize them as coccobacilli. Gray, weakly beta-hemolytic colonies on blood agar plates. Tumbling motility, which makes it appear as if it's doing summersaults in broth media. Facultative intracellular anaerobes. Adhesion and invasion, vacuole escape, and movement are regulated by positive regulatory factor (PrfA), a transcription factor that is activated upon host cell infection. These virulence factors allow L. monocytogenes to move from the lumen of the gut to infect the meninges and other body tissues. Internalins A & B facilitate attachment and entry into host cells: Internalin A recognizes receptors on host enterocytes. Internalin B interacts with a wider range of cells, including endothelial cells, fibroblasts, and enterocytes. Listeriolysin O and Phospholipase C: Upon entry into the host cell, bacteria release listeriolysin O and phospholipase C to escape from vacuoles. This promotes microbial evasion of phagolysosome destruction and access to the cytosol for reproduction. Actin assembly-inducing protein (ActA) facilitates intra- and intercellular movement via "comet tails". – ActA is also associated with aggregation and biofilm formation, and avoidance of autophagy. 1. Ingestion of L. monocytogenes-contaminated foods. 2. Interalins facilitate entry to enterocytes from the lumen of the GI tract. 3. Actin tails push the bacteria out of enterocytes and to macrophages, where replication occurs. 4. The parasitized macrophages disseminate the bacteria throughout the body. 5. Ultimately, L. monocytogenes can cross the blood-brain barrier and cause meningitis. Infection with L. monocytogenes can induce a range of dysfunction: some individuals are asymptomatic carriers, while others, particularly those with defective cellular immunity, experience disease. Healthy adults: flu-like symptoms and gastroenteritis with watery diarrhea, fever, aches, and abdominal cramps. Immunocompromised adults, including pregnant women, the elderly, and transplant recipients: bacteremia and meningitis can develop. L. monocytogenes meningitis is associated with high mortality. Neonate: Early and late onset diseases: Early onset infection occurs when the bacteria cross the placenta; this can result in spontaneous abortion, pre-term birth, or granulomatosis infantiseptica, which is characterized by rash, abscesses and granulomas in the liver, lungs, spleen, and other organs. Late-onset infection is acquired during or soon after birth, and can result in meningitis that appears up to a month after birth. Because L. monocytogenes is ubiquitous in the environment, and there is no vaccine, prevention is difficult. At-risk populations, including pregnant women, are advised to avoid unpasteurized dairy foods and cold deli foods. Invasive infections can be treated with ampicillin and gentamicin.