Which organism has a special predilection towards placenta?
**Core Concept**
Listeriosis is a zoonotic infection caused by Listeria monocytogenes, a gram-positive bacterium. The organism has a special predilection towards the placenta, particularly affecting pregnant women, causing listeriosis.
**Why the Correct Answer is Right**
Listeria monocytogenes can invade the placenta and cause intrauterine infection, leading to preterm labor, fetal death, or neonatal sepsis. The bacteria exploit the placental barrier by invading trophoblasts and maternal macrophages, facilitating vertical transmission to the fetus. This mechanism is crucial for understanding the pathogenesis of listeriosis in pregnancy.
**Why Each Wrong Option is Incorrect**
**Option A:** Escherichia coli (E. coli) is a common cause of urinary tract infections and neonatal sepsis but does not have a special predilection towards the placenta.
**Option B:** Toxoplasma gondii is a protozoan parasite that can cause congenital toxoplasmosis, but it primarily targets the fetus through vertical transmission, rather than the placenta directly.
**Option C:** Streptococcus agalactiae (Group B streptococcus) is a common cause of neonatal sepsis and meningitis but is not specifically associated with placental invasion.
**Clinical Pearl / High-Yield Fact**
Listeriosis in pregnancy is a medical emergency requiring prompt treatment with antibiotics, such as ampicillin or gentamicin, to prevent fetal and maternal complications.
**Correct Answer:** A. Listeria monocytogenes.