Bacterial Communities in the Womb During Healthy Pregnancy

Abstract

The idea that healthy uterine cavity is sterile is challenged nowadays. It is still debatable whether the bacteria present in the uterine cavity during pregnancy are residents or invaders. To reveal microbiome composition and its characteristics in the womb of pregnant women, 41 decidual tissue samples and 64 amniotic fluid samples were taken from pregnant Chinese women. DNA extraction was followed by pyrosequencing of the hypervariable V4 region of the 16S rDNA gene to characterize womb microbiome. Both types of samples had low diversity microbiome with Enterobacteriaceae being the dominant phylotypes at family level. To characterize the nature of colonization during pregnancy, the presence of endogenous biomass was confirmed by cultivation. Surprisingly, all of the 50 amniotic fluid samples studied were culture-negative, whereas 379 out of 1,832 placenta samples were culture-positive. Our results suggested that womb contained microbiome with low diversity. Culture-based investigation of amniotic fluid and placenta samples confirmed the presence of cultivable microorganisms in the placenta but not in amniotic fluid. Thus it suggests that bacterial colonization does occur during healthy pregnancy.

Keywords: V4 region of 16S rDNA; amniotic fluid; decidual tissue; firmicutes; microbiome; proteobacteria.

FIGURE 1

Bacterial profiling and diversity in each sample analyzed by 16S rDNA gene pyrosequencing. (A) Bacterial profiling plot of relative abundances of operational taxonomic units (OTUs) at the family level. Points plot of Estimators of the Shannon index are shown below. (B) Difference of bacterial taxa at the genus level between decidual tissue and amniotic fluid samples. (C) Non-metric multidimensional scaling of microbiome structure based on weighted UniFrac distance. Relative abundances of OTUs accounting for >0.1% of the total bacterial community are shown.