The goal of the paper was to determine whether such conditions, as pre-eclamsia, preterm birth and delivery of infants small for gestational age, were associated with presence of the microbial DNA in the placenta. The authors of the paper collected and analyzed 537 placentas, and did not find evidence for the placental microbiome existence. Furthermore, five different ways of microbial contamination of the samples were tested: contamination with bacteria during labor and delivery; contamination of tissue samples when washed with Phosphate-Buffered Saline (PBS); contamination during DNA extraction, amplification and/or sequencing steps. The only bacterium that was found to be present in placenta before the onset of labor was Streptococcus agalactiae which was detected by three different methods: 16S rRNA sequencing, shotgun metagenomics and qPCR. Despite of being a known pathogen, S. agalactiae has not been found to be associated with any of the harmful pregnancy conditions. The paper concludes that there is no placental microbiome, however there is a possibility that colonization with pathogens can lead to adverse pregnancy outcomes.
Link to the paper