Inhibition of group B streptococci by amniotic fluid from patients with intra-amniotic infection and from control subjects.

This study describes the inhibition of group B streptococci by amniotic fluid from 50 patients with intra-amniotic infection and 50 matched, noninfected control subjects. Patients were matched for gestational age, time from rupture of membranes to delivery, and time from rupture of membranes to collection of the sample of fluid. Study patients had the clinical diagnosis of intra-amniotic infection and greater than or equal to 10(2) colony-forming units of a high-virulence organism per milliliter. None of the control patients became infected or received antibiotics. We collected the amniotic fluid in the study patients prior to antibiotic therapy. A comparison of bacterial growth in the amniotic fluid versus the amniotic fluid plus phosphate showed that only eight (16%) of the intra-amniotic infection samples of fluid were inhibitory, whereas 18 (36%) of the control samples of fluid were inhibitory (X2 = 5.20, p less than 0.02). However, a comparison of group B streptococci growth in amniotic fluid and Todd-Hewitt broth did not show a statistically significant difference. We conclude that the amniotic fluid bacterial inhibitory assay with group B streptococci is technically more difficult to perform and interpret.