Listeria monocytogenes vs Group B Streptococcus
How to tell Listeria monocytogenes and Group B Streptococcus apart when a board question makes them look alike.
Listeria is foodborne rod with tumbling motility; GBS is maternal-colonization coccus with CAMP positivity.
Side by side
Foodborne gram-positive rod with tumbling motility; severe disease in pregnancy, neonates, older adults, and immunocompromised patients.
Beta-hemolytic CAMP-positive gram-positive coccus from maternal genital colonization causing neonatal sepsis, pneumonia, and meningitis.
Listeria survives intracellularly and spreads cell-to-cell using actin polymerization.
GBS colonizes maternal genital tract and invades newborn bloodstream or CNS during early or late neonatal disease.
Soft cheese/deli meat exposure, tumbling motility, or gram-positive rods point Listeria.
Maternal rectovaginal screen, CAMP positivity, or beta-hemolytic cocci in neonate points Group B Strep.
The trap
Both can cause neonatal meningitis, so morphology and maternal exposure history are decisive.
The repair move
For neonatal meningitis or sepsis, sort by gram stain and exposure: (1) gram-positive ROD with characteristic tumbling motility at 22 degrees C plus growth at 4 degrees C (cold enrichment) plus dietary history of unpasteurized dairy, deli meats, or soft cheeses equals Listeria monocytogenes (treat with ampicillin plus gentamicin; classically affects neonates from vertical transmission, pregnant women, immunocompromised adults, and elderly; intracellular pathogen using actin-based motility); (2) gram-positive COCCUS in chains, beta-hemolytic, bacitracin-resistant, CAMP test positive, hippurate positive, in a neonate of a maternally-colonized mother equals Group B Streptococcus / S agalactiae (treat with penicillin or ampicillin; screen all pregnant women at 35 to 37 weeks gestation; intrapartum penicillin if culture positive or risk factors present). Both are covered by empiric neonatal meningitis regimen of ampicillin plus gentamicin (or cefotaxime).
Try a free question
CoreA pregnant patient with fever and diarrhea after soft cheese exposure develops bacteremia. The organism is a gram-positive rod with tumbling motility that can cross the placenta. Which organism is most likely?
Show answer and explanation
Answer: A. Listeria monocytogenes. Listeria is a gram-positive rod with tumbling motility, foodborne exposure, intracellular survival, and risk in pregnancy/neonates/elderly.
Why the other choices are tempting
- B. Group B Streptococcus is a gram-positive coccus causing neonatal sepsis after maternal genital colonization.
- C. E coli is a gram-negative rod and major neonatal meningitis cause, especially K1 strains.
- D. S pneumoniae is a lancet-shaped diplococcus.
- E. H influenzae is a gram-negative coccobacillus requiring X and V factors.
Flashcards
Tap a card to flip it.
What is the fastest separator for Listeria monocytogenes vs Group B Streptococcus?
Listeria is foodborne rod with tumbling motility; GBS is maternal-colonization coccus with CAMP positivity.
What clue should make you choose Listeria monocytogenes?
Foodborne gram-positive rod with tumbling motility; severe disease in pregnancy, neonates, older adults, and immunocompromised patients.
Quick answers
What is the fastest way to tell Listeria monocytogenes from Group B Streptococcus?
Listeria is foodborne rod with tumbling motility; GBS is maternal-colonization coccus with CAMP positivity.
What is the key clue for Listeria monocytogenes?
Foodborne gram-positive rod with tumbling motility; severe disease in pregnancy, neonates, older adults, and immunocompromised patients.
What is the key clue for Group B Streptococcus?
Beta-hemolytic CAMP-positive gram-positive coccus from maternal genital colonization causing neonatal sepsis, pneumonia, and meningitis.
What is the common trap with Listeria monocytogenes vs Group B Streptococcus?
Both can cause neonatal meningitis, so morphology and maternal exposure history are decisive.