Effect of bacterial growth on the bursting pressure of fetal membranes in vitro.

By mounting a layer of chorioamniotic membrane on a specially designed reaction vessel, we studied the effect of Escherichia coli and/or group B streptococcus growing on the decidual surface of the membranes in tissue culture or bacteriologic medium. The organisms grew equally well in either medium. When growing in tissue culture medium, either organism significantly weakened the membranes as compared with controls (membranes incubated in the absence of either organism). Membranes derived from pregnancies delivered vaginally or abdominally responded similarly. When organisms were grown in bacteriologic medium, bursting pressures did not decrease. Addition of bacteriologic medium (20-60%) to tissue culture medium did not affect bacterial growth, but inhibited significantly the lowering of bursting pressures. Bacteriologic medium also inhibited the peroxidase-H2O2-halide system in vitro. Heat-killed bacteria and/or supernatants of culture medium previously inoculated with bacteria were not effective in weakening membranes. The results suggest that live bacteria in conjunction with active membrane metabolism lead to a weakening and eventual rupture of the membranes.