Characterization of Group B Streptococcal Invasion of Human Chorion and Amnion Epithelial Cells In Vitro

Group B streptococci (GBS) have been cultured from the chorioamnionic membrane of pregnant women, usually in association with chorioamnionitis and premature labor (K. A. Boggess, D. H. Watts, S. L. Hillier, M. A. Krohn, T. J. Benedetti, and D. A. Eschenbach, Obstet. Gynecol. 87:779–784, 1996). Colonization and infection of placental membranes can be a prelude to neonatal GBS infections even in the presence of intact membranes (R. L. Naeye and E. C. Peters, Pediatrics 61:171–177, 1978), suggesting that GBS cause chorioamnionitis or establish amniotic fluid infections by partial or complete penetration of the placental membranes. We have isolated and grown cultures of primary chorion and amnion cells from human cesarean-section placentas. This has provided a biologically relevant model for investigating GBS adherence to and invasion of the two epithelial barriers of the placental membrane. GBS adhered to chorion cell monolayers to a high degree. Pretreatment of GBS with trypsin reduced adherence up to 10-fold, which suggested that the bacterial ligand(s) was a protein. GBS invaded chorion cells at a high rate in vitro, and invasion was dependent on cellular actin polymerization. GBS could be seen within intracellular vacuoles of chorion cells by transmission electron microscopy. We also demonstrated that GBS were capable of transcytosing through intact chorion cell monolayers without disruption of intracellular junctions. GBS also adhered to amnion cells; in contrast, however, these bacteria failed to invade amnion cells under a variety of assay conditions. GBS interactions with the chorion epithelial cell layer shown here correlate well with epidemiological and pathological studies of GBS chorioamnionitis. Our data also suggest that the amnion cell layer may provide an effective barrier against infection of the amniotic fluid.