A 28-year-old primigravid woman at 31 weeks' gestation comes to the physician because of fever, myalgia, abdominal pain, nausea, and diarrhea for 3 days. Her pregnancy has been uncomplicated. Her only medication is a prenatal vitamin. Her temperature is 39.4°C (102.9°F). Physical examination shows diffuse abdominal pain. Blood cultures incubated at 4°C (39.2°F) grow a gram-positive, catalase-positive organism. Which of the following is the major virulence factor of the organism responsible for this patient's clinical presentation?

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Eductional Objective: Listeria monocytogenes is a facultative intracellular, gram-positive rod that most often causes febrile gastroenteritis.  Pathogenesis is mediated largely by listeriolysin O, an enzyme that creates pores in phagosomes, which allows the bacteria to escape lysosomal destruction.  Pregnant women in the third trimester are at greatest risk; infection increases the risk of fetal demise, early labor, and neonatal infection.

A 28-Year-Old Primigravid Woman at 31 Weeks' Gestation Comes to the Physician