Bacterial growth inhibition by amniotic fluid. V. Phosphate-to-zinc ratio as a predictor of bacterial growth-inhibitory activity.

Human amniotic fluid has been shown to contain an inorganic bacterial growth-inhibitory component, zinc. The average zinc concentration in amniotic fluid was 0.44 mug per milliliter. The phosphate concentration of amniotic fluid appears to determine the expression of zinc inhibitory activity. The average phosphate concentration was 92 mug per milliliter. For 22 fluid samples tested, a phosphate-to-zinc ratio of 100 or less predicted a bactericidal fluid. A ratio between 100 and 200 predicted a bacteriostatic fluid. A ratio of greater than 200 predicted a noninhibitory fluid. The possible clinical significance of the ratio is discussed.