A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
An 8-day-old male infant presents to the pediatrician with a high-grade fever and poor feeding pattern with regurgitation of milk after each feeding. On examination the infant showed abnormal movements, hypertonia, and exaggerated DTRs. The mother explains that during her pregnancy, she has tried to eat only unprocessed foods and unpasterized dairy so that her baby would not be exposed to any preservatives or unhealthy chemicals. Which of the following characteristics describes the causative agent that caused this illness in the infant?
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A
Gram-positive, facultative intracellular, motile bacilliCorrect. Listeria monocytogenes is a gram-positive, facultatively intracellular, motile bacillus that causes neonatal meningitis after maternal exposure to unpasteurized dairy — exactly this scenario.
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B
Gram-positive, catalase-negative, beta hemolytic, bacitracin resistant cocciIncorrect. This describes group B Streptococcus (S. agalactiae) — also a neonatal meningitis pathogen, but it is a gram-positive coccus and the exposure history fits Listeria, not GBS.
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C
Gram-negative, lactose-fermenting, facultative anaerobic bacilliIncorrect. This describes E. coli, which can cause neonatal sepsis/meningitis but is a gram-negative bacillus and is not specifically linked to unpasteurized dairy.
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D
Gram-negative, maltose fermenting diplococciIncorrect. This describes Neisseria meningitidis, which causes meningitis in older children/adults, not 8-day-old neonates, and does not have this maternal-food link.
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E
Gram-positive, catalase-positive, coagulase-positive cocci in clustersIncorrect. This describes Staphylococcus aureus, which causes neonatal skin and bloodstream infections but is not specifically transmitted through unpasteurized dairy or characteristically associated with neonatal meningitis from this exposure.
↑ Tap an answer to reveal the reasoning
Answer: A. An 8-day-old neonate with fever, poor feeding, hypertonia, and exaggerated reflexes — a meningoencephalitis picture — in the setting of maternal consumption of unpasteurized dairy points to Listeria monocytogenes. Listeria is a leading cause of neonatal meningitis in the first month of life (along with group B Strep and E. coli) and is acquired transplacentally or during passage through the birth canal after maternal foodborne infection. Pregnant women are roughly 10-fold more susceptible because of attenuated cell-mediated immunity.
Listeria is a gram-positive, facultatively intracellular, motile (tumbling motility at 22°C), beta-hemolytic, catalase-positive bacillus. Intracellular survival uses listeriolysin O to escape the phagosome and actin-based 'rocket' motility for cell-to-cell spread. It also notably grows at refrigerator temperatures (cold enrichment).
Treatment is ampicillin (often with gentamicin for synergy). Prevention in pregnancy means avoiding soft cheeses, deli meats, unpasteurized dairy, and undercooked foods — precisely what this mother was advised against.
**Why each option:**
**A.** Listeria monocytogenes is a gram-positive, facultatively intracellular, motile bacillus that causes neonatal meningitis after maternal exposure to unpasteurized dairy — exactly this scenario.
**B.** This describes group B Streptococcus (S. agalactiae) — also a neonatal meningitis pathogen, but it is a gram-positive coccus and the exposure history fits Listeria, not GBS.
**C.** This describes E. coli, which can cause neonatal sepsis/meningitis but is a gram-negative bacillus and is not specifically linked to unpasteurized dairy.
**D.** This describes Neisseria meningitidis, which causes meningitis in older children/adults, not 8-day-old neonates, and does not have this maternal-food link.