Antibacterial activity in human amniotic fluid: dependence on divalent cations.

Antibacterial activity, tested against Bacillus subtilis, was present in all 34 samples of human amniotic fluid collected between 37 and 41 weeks gestation. High-molecular-weight (beta-lysin) antibacterial activity was reduced after treatment with ethylene diamine tetra-acetic acid (EDTA), but not after treatment with 1, 10-phenanthroline or diphenylthiocarbazone. The activity was restored following incubation with magnesium, calcium, or zinc. Low-molecular-weight antibacterial activity (less than 1000 daltons) in acid-alcohol extracts was reduced after treatment with dithizone, but not after treatment with EDTA or 1, 10 phenanthroline. Activity was restored after treatment with manganese, cobalt or zinc. High-molecular-weight (beta-lysin) activity was therefore biochemically similar to serum beta-lysin but biochemically different from the low-molecular-weight antibacterial component of amniotic fluid.