Listeria monocytogenes favors the vacuolar compartment during ex vivo human placental infections.

In ex vivo human placental infections, Listeria monocytogenes primarily remains within Listeria-containing vacuoles, with actin-rich structures essentially absent (<1%).

• Why it matters: Cultured-cell models predict rapid LCV escape, cytoplasmic replication, and actin-based spread, but it was unknown whether these steps occur in intact human placental tissue.
• What they did: Using ex vivo placental infections, the study quantified actin-rich structures and tracked bacterial localization by quantitative histology and immunofluorescence, including Rab5- and Lamp1-positive vacuoles.
• The result: 39% of wild-type bacteria remained within Rab5-positive vacuoles and 44% in Lamp1-positive vacuoles, while only 1%–4% were seen in cultured placental cells, and most vacuoles lacked vATPase and cathepsin B.