Bacteria and inflammatory cells reduce chorioamniotic membrane integrity and tensile strength

Bacteria and the inflammatory response they engender are implicated in the pathophysiology of premature rupture of fetal membranes and preterm birth. We tested the hypothesis that bacteria and polymorphonuclear neutrophils may have both separate and combined effects in weakening the amniochorionic membrane, and thus predispose to premature rupture of membranes. We examined how three parameters of membrane integrity (bursting tension, work to rupture, and elasticity) were affected by standardized preparations (10(9) cfu/mL) of group B streptococci or Staphylococcus aureus in the presence or absence of purified human neutrophils (32 x 10(6)/mL). In addition, effects of purified human neutrophil elastase were evaluated. Exposure to either group B streptococcus or S aureus decreased membrane strength, elasticity, and work to rupture. Only activated neutrophils had significant effects on membrane strength. Membrane exposure to S aureus plus neutrophils led to an additive weakening of fetal membranes. On the other hand, group B streptococci did not interact with neutrophils to yield a significant further weakening of the membranes. Elastase (150 U/mL) also weakened the membrane. The results were correlated with measures of protease (Azocoll and ninhydrin assays) and peroxidase (dimethoxybenzidine) activity. Our findings support the concept that human neutrophils and their constituent enzymes may act in concert with bacteria and their protease(s) in weakening amniochorion, and may possibly predispose to premature rupture of membranes in some women. These observations require clinical correlations.