The effect of meconium staining of amniotic fluid on the growth of Escherichia coli and group B streptococcus.
OBJECTIVE
To compare the effect of meconium staining on the growth rate of Escherichia coli and group B streptococci (GBS) in amniotic fluid.


METHODS
Sterile meconium was added in different concentrations to pooled sterile amniotic fluid obtained from term mothers. Meconium concentration was equal to: 1, 1.5, 3, 6, and 12 mg meconium/ml amniotic fluid. Amniotic fluid was quantitatively inoculated with E. coli and GBS type II and type III organisms (10(3) organisms/ml). Clear amniotic fluid and Todd-Hewitt broth served as controls. Growth rates of organisms were measured at 2, 4, 6, 8, and 24 hours after inoculation.


RESULTS
Clear amniotic fluid was completely inhibitory for growth of E. coli even after 24 hours of incubation. In contrast, after 6 hours of incubation, significantly increased growth of GBS occurred (10(5) organisms/ml) (p<0.0001). The inhibitory effect on E. coli was observed even with meconium concentration of up to 1.5 mg/ml. In contrast, even the smallest concentration of meconium (1 mg/ml) resulted in a 2-log fold increase of GBS within 4 hours. The more rapid growth rate of GBS compared to E. coli persisted even at moderate staining of amniotic fluid (6 mg/ml) in the first 8 hours of incubation (p<0.005). In the presence of thick meconium (12 mg/ml), during the first 6 hours of incubation, the growth rates of GBS and E. coli were nearly similar.


CONCLUSIONS
GBS (type II and III) growth, in contrast to E. coli, was less inhibited by amniotic fluid, occurred at a more rapid rate, and was enhanced at lower concentrations of meconium. As such, the presence of even light meconium staining in cases of rupture of membranes of even less than 6 hours in a mother who is a GBS carrier should be considered as a risk factor for the development of perinatal GBS infection.
Eidelman
Arthur I
AI
Department of Neonatology, Shaare Zedek Medical Center, Hebrew University School of Medicine, Jerusalem, Israel.
Nevet
Ayelet
A
Rudensky
Bernard
B
Rabinowitz
Ron
R
Hammerman
Cathy
C
Raveh
David
D
Schimmel
Michael S
MS
D000653:Amniotic Fluid; D015169:Colony Count, Microbial; D003470:Culture Media; D004926:Escherichia coli / Q000254:growth & development*; D005260:Female; D006801:Humans; D008470:Meconium; D011247:Pregnancy; D011336:Probability; D012680:Sensitivity and Specificity; D013292:Streptococcus agalactiae / Q000254:growth & development*
D003470:Culture Media