Which statement best describes Listeria crossing barriers?

Which statement best describes Listeria crossing barriers?

• A. It forms spores to survive in harsh environments
• B. It seeds the bloodstream...
• C. It uses flagellin to invade from gut lumen
• D. It invades through internalin-mediated invasion and can disseminate to placenta causing fetal infection

Answer: (D)

Listeria crosses barriers by using invasion proteins called internalins to enter host cells, then spreads from cell to cell and can reach distant sites such as the placenta, where it can cause fetal infection. This internalin-mediated invasion with possible placental dissemination captures the key pathogenesis: intestinal invasion, escape into the cytosol, and hematogenous spread to the placenta leading to fetal infection. The other ideas don’t fit as the primary mechanism: it does not form spores; bacteremia can occur but crossing barriers is driven by intracellular invasion rather than mere bloodstream seeding; and invasion is not driven by flagellin-based motility—the invasion process relies on internalins and related intracellular spread.

Listeria crosses barriers by using invasion proteins called internalins to enter host cells, then spreads from cell to cell and can reach distant sites such as the placenta, where it can cause fetal infection. This internalin-mediated invasion with possible placental dissemination captures the key pathogenesis: intestinal invasion, escape into the cytosol, and hematogenous spread to the placenta leading to fetal infection. The other ideas don’t fit as the primary mechanism: it does not form spores; bacteremia can occur but crossing barriers is driven by intracellular invasion rather than mere bloodstream seeding; and invasion is not driven by flagellin-based motility—the invasion process relies on internalins and related intracellular spread.