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Am J Obstet Gynecol. 2019 Mar;220(3):267.e1-267.e39. doi: 10.1016/j.ajog.2018.10.018.

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

Author information

1
Department of Biochemistry, Microbiology and Immunology, Wayne State University School of Medicine, Detroit, MI; Perinatal Research Initiative in Maternal, Perinatal and Child Health, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI. Electronic address: ktheis@med.wayne.edu.
2
Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI; Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI; Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, MI. Electronic address: prbchiefstaff@med.wayne.edu.
3
Department of Biochemistry, Microbiology and Immunology, Wayne State University School of Medicine, Detroit, MI; Perinatal Research Initiative in Maternal, Perinatal and Child Health, Wayne State University School of Medicine, Detroit, MI.
4
Department of Biochemistry, Microbiology and Immunology, Wayne State University School of Medicine, Detroit, MI; Perinatal Research Initiative in Maternal, Perinatal and Child Health, Wayne State University School of Medicine, Detroit, MI; Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI.
5
Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Department of Physiology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI.
6
Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI.
7
Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI; Department of Obstetrics and Gynecology, Soroka University Medical Center, School of Medicine, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
8
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA; Department of Obstetrics and Gynecology, Virginia Commonwealth University, Richmond, VA.
9
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA; Center for Microbiome Engineering and Data Analysis, Virginia Commonwealth University, Richmond, VA.
10
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA.
11
Department of Obstetrics and Gynecology, Virginia Commonwealth University, Richmond, VA.
12
Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI; Maternity Department "D" and Obstetrical Day Care Center, Division of Obstetrics and Gynecology, Soroka University Medical Center, Ben Gurion University of the Negev, Beer-Sheva, Israel.
13
Perinatal Research Initiative in Maternal, Perinatal and Child Health, Wayne State University School of Medicine, Detroit, MI; Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI; Department of Physiology, Wayne State University School of Medicine, Detroit, MI; Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD, and Detroit, MI.

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 background-contaminating 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 indicate greater abundances of bacterial 16S ribosomal RNA genes in placental tissues than in technical controls. Therefore, there was no evidence of the presence of microorganisms above background contamination from reagents in the placentas. (3) 16S ribosomal RNA gene sequencing did not reveal consistent differences in the composition or structure of bacterial profiles between placental samples and background technical controls. (4) Most of the bacterial sequences obtained from metagenomic surveys of placental tissues were from cyanobacteria, aquatic bacteria, or plant pathogens, which are microbes unlikely to populate the human placenta. Coprobacillus, which constituted 30.5% of the bacterial sequences obtained through metagenomic sequencing of placental samples, was not identified in any of the 16S ribosomal RNA gene surveys of these samples. These observations cast doubt as to whether this organism is really present in the placenta of patients at term not in labor.

CONCLUSION:

With the use of multiple modes of microbiologic inquiry, a resident microbiota could not be identified in human placentas delivered at term from women without labor. A consistently significant difference in the abundance and/or presence of a microbiota between placental tissue and background technical controls could not be found. All cultures of placental tissue, except 1, did not yield bacteria. Incorporating technical controls for potential sources of background-contaminating DNA for studies of low microbial biomass samples, such as the placenta, is necessary to derive reliable conclusions.

KEYWORDS:

bacteria; bacterial culture; contamination; low microbial biomass sample; microbiome; microorganism; pregnancy; tissue

PMID:
30832984
PMCID:
PMC6733039
[Available on 2020-03-01]
DOI:
10.1016/j.ajog.2018.10.018

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