Chorioamniotic membranes constitute a competent barrier to group b streptococcus in vitro

Objective: To study the penetration of group B streptococcus (GBS) through human chorioamniotic membranes in vitro. Study design: Chorioamniotic membranes from seventeen healthy women were mounted onto glass cylinders and placed in tissue culture trays constituting a two-compartment system with a maternal compartment internally and a fetal compartment externally. GBS from healthy pregnant women and from newborn babies with sepsis were added to the maternal compartment at densities from 10 7 to 10 9 colony forming units (cfu) per ml. Results. Irrespective of inoculum density, GBS was not recovered from the fetal compartment within a 20 h incubation period. By histology, micro-colonies of GBS were found on the maternal surface after 8 h, but invasion of the morphologically intact membranes was not observed. A five log reduction in cfu occurred in the maternal compartment with amnion when GBS were suspended in saline. Conclusion: In this in vitro model the membranes appear to constitute an effective barrier against ascending infection.