Antibiotic inhibition of bacterially induced fetal membrane weakening.

A fetal membrane model was used to evaluate in vitro the efficacy of two antibiotics, erythromycin and clindamycin, in preventing bacterial protease-induced weakening of amniochorion. Standardized inocula of protease-producing bacteria (10(9) colony-forming units [cfu]/mL Staphylococcus aureus, incubated at 37C for 20 hours) reliably reduced fetal membrane structural integrity as reflected by bursting tension and work to rupture. Supraminimal inhibitory concentrations (supra-MICs) (erythromycin 0.23 microgram/mL; clindamycin 0.56 microgram/mL) and subminimal inhibitory concentrations (sub-MICs) (erythromycin 0.13 microgram/mL; clindamycin 0.06 microgram/mL) of both antibiotics prevented fetal membrane impairment due to test bacteria. Supra-MICs of both antibiotics prevented bacterial cell growth and release of protease. Sub-MICs of both antibiotics allowed bacterial cell growth of test microorganisms but inhibited protease release and subsequent fetal membrane damage. These findings suggest that inhibitory and even subinhibitory doses of antibiotics such as erythromycin and clindamycin may be effective in reducing the occurrence of premature rupture of membranes and subsequent preterm birth mediated by susceptible microorganisms.