Does the human placenta delivered at term have a microbiota? Results of cultivation, quantitative real-time PCR, 16S rRNA gene sequencing, and metagenomics

Abstract

BACKGROUND: The human placenta has been traditionally viewed as sterile, and microbial invasion of this organ has been associated with adverse pregnancy outcomes. Yet, recent studies that utilized sequencing techniques reported that the human placenta at term contains a unique microbiota. These conclusions are largely based on the results derived from the sequencing of placental samples. However, such an approach carries the risk of capturing background-contaminating DNA (from DNA extraction kits, polymerase chain reaction reagents, and laboratory environments) when low microbial biomass samples are studied. OBJECTIVE: To determine whether the human placenta delivered at term in patients without labor who undergo cesarean delivery harbors a resident microbiota ("the assemblage of microorganisms present in a defined niche or environment"). STUDY DESIGN: This cross-sectional study included placentas from 29 women who had a cesarean delivery without labor at term. The study also included technical controls to account for potential backgroundcontaminating DNA, inclusive in DNA extraction kits, polymerase chain reaction reagents, and laboratory environments. Bacterial profiles of placental tissues and background technical controls were characterized and compared with the use of bacterial culture, quantitative real-time polymerase chain reaction, 16S ribosomal RNA gene sequencing, and metagenomic surveys. RESULTS: (1) Twenty-eight of 29 placental tissues had a negative culture for microorganisms. The microorganisms retrieved by culture from the remaining sample were likely contaminants because corresponding 16S ribosomal RNA genes were not detected in the same sample.(2) Quantitative real-time polymerase chain reaction did not

Separating the signal from the noise in metagenomic cell-free DNA sequencing

“…were detected in the normal pregnancy group (Fig. 2d), in line with recent studies that point to a sterile 24 amniotic cavity and placenta in the absence of infection 30,31 . The cfDNA sequencing assay detected only 25 six of the fourteen bacterial genera identified by bacterial culture or PCR/ESI-MS, and was unable to 26 identify a fungal pathogen, Candida albicans, detected by PCR/ESI-MS (see Methods).…”

“…Here, we report Low Biomass Background Correction (LBBC), a bioinformatics noise 28 filtering tool informed by the uniformity of the coverage of microbial genomes and the batch variation in 29 the absolute abundance of microbial cfDNA. We demonstrate that LBBC leads to a dramatic reduction in 30 false positive rate while minimally affecting the true positive rate for a cfDNA test to screen for urinary 31 tract infection. We next performed high throughput sequencing of cfDNA in amniotic fluid collected from 32…”

The composition of the perinatal intestinal microbiota in horse

“…The maternal microbiota affects the development of the intestinal immune system already in the fetal period 4 . This is mediated by circulating microbial metabolites 4 and possibly also by small numbers of microbial cells translocating to the fetus via placenta [5][6][7] . The major microbial colonization occurs at birth.…”

Influence of maternal microbiota during pregnancy on infant immunity

“…Vertical transmission of microbes from various maternal body sites contribute to the developing infant gut microbiota, including the gut, vagina, skin and breast milk [1,2]. This dogma has since been challenged [5][6][7][8], with unique placental microbiome in some studies [5,9] but not others [7,10]. Historically, it has been assumed that the uterine environment is sterile [4].…”

“…Historically, it has been assumed that the uterine environment is sterile [4]. This dogma has since been challenged [5][6][7][8], with unique placental microbiome in some studies [5,9] but not others [7,10].…”