E. coli growth inhibition by amniotic fluid.

Amniotic fluid samples were collected aseptically from 29 normal pregnancies, between the 38th and 41st week of gestation and checked for sterility in the laboratory, in order to investigate in vitro the effect of the liquor on the growth of E. coli. Brain Heart Infusion (B.H.I.) and Ringer solution were used as controls. E. coli cultures were inoculated in amniotic fluid, B.H.I., Ringer solution and amniotic fluid plus B.H.I. and incubated at 37degreesC for 48 hours. At 0, 1, 3, 6, 12, 24, 36 and 48 hours of incubation, surface viable counts were performed to estimate the number of E. coli viable cells. The growth of E. coli in B.H.I. started furing the 1st hours after inoculation and continued over 48 hours; in Ringer solution the mean growth curve and almost identical to that of B.H.I. In amniotic fluid the growth of E. coli began from the 1st hour of inoculation but the growth curve was much lower, became static in 24 hours and a permanent inhibition was observed thereafter. The addition of a small amount of B.H.I. in amniotic fluid enhanced the growth of E. coli, but the growth curve was lower in comparison to the curves of the two controls studied. In conclusion, after 48 hours of inoculation in amniotic fluid, 26 of the 29 cases showed bacteriostatic or bactericidal activity of the liquor upon the growth of E. coli.