A Case of Intrauterine Listeria Infection During Pregnancy: NanoSuit Imaging of Listeria monocytogenes in the Amniotic Membrane

Listeriosis during pregnancy is rare but can lead to premature miscarriage and intrauterine fetal death. A 29-year-old pregnant woman at 29 weeks of gestation was transferred to our hospital because of mild fever and abdominal pain. Emergency cesarean section was performed due to non-reassuring fetal status concomitant with suspected intrauterine infection. An unusually bright yellow amniotic fluid was observed. The oropharyngeal cavity of the neonate was occupied by thick, tenacious yellow mucus, making its removal challenging. The neonate was intubated due to poor oxygenation. Neonatal blood cultures revealed <i>Listeria monocytogenes</i>. Gram staining of cerebrospinal fluid was negative. The neonate was treated and discharged on the 65th day after birth. The mother had a fever of 39.4°C on the first day after surgery; however, no other significant incident occurred. She was discharged on the 10th day after surgery. Placental pathology revealed funisitis, chorioamnionitis, and marginal deciduitis without evidence of villitis, suggesting predominant transvaginal rather than hematogenous infection. Scanning electron microscopy using NanoSuit imaging revealed <i>Listeria</i> <i>monocytogenes</i> in the amniotic epithelium. The presence of <i>Listeria</i> <i>monocytogenes</i> has been reported in foods stored in refrigerators for extended periods of time and in ready-to-eat meals; therefore, it is difficult for pregnant women to be aware of all potential risks. It is important for physicians to recognize that listeriosis may have a long incubation period and present with mild maternal symptoms. Nevertheless, it should be considered as a differential diagnosis. Routine and prompt identification of the causative organism through amniotic fluid and placental swab cultures is important, particularly when intrauterine infection is suspected. Moreover, pathological examination of the placenta can provide insights into the potential route of infection.