Deep microbial analysis of multiple placentas shows no evidence for a placental microbiome

Abstract

Objectives To resolve the controversy regarding the presence of a microbiota in the placenta.Design Classical and molecular microbiological study.Setting All samples were collected during caesarean section.Population A total of 28 human placentas and six murine placentas.Methods All 28 human placentas were checked for 16S rRNA gene amplification products. Three locations from four selected human placentas and three 'environmental controls' for each placenta were placed in seven culture media. The four selected human placentas were further analysed using Gram stain, immunohistochemistry for bacteria, electron microscopy, and TaqMan RT-qPCR. Six placentas from three SPF mice were cut into four pieces each, and further analysed for 16S rRNA gene amplification.Main outcome measures Microbiological and molecular evidence of bacteria.Results None of the placental cultures used for the full analysis, or their environmental cultures, was positive for bacterial growth. None of the other methods showed any evidence of bacteria. Immunohistochemistry showed negligible bacterial counts. None of the murine placentas showed evidence of 16S rRNA gene amplification.Conclusions Our results support that the fetal environment in the womb is sterile. Based on the immunohistochemistry and the limit of detection of the other methods used, if a placental microbiome exists, it is of extreme low biomass, and thus its effect on clinical phenotypes is probably minor, if it exists at all.Tweetable abstract Using several microbiological and molecular methods in parallel, we found no compelling evidence of bacteria in human and mouse placentas.

No consistent evidence for microbiota in murine placental and fetal tissues

“…Herein, the murine placenta and fetal tissues did not yield substantive 16S rRNA gene sequence libraries, while the maternal sites other than the uterus, heart, and liver consistently did so. These results are consistent with those of Kuperman et al (18), in which 30 cycles of PCR did not yield discernible amplicons from murine placental tissue. Notably, in our study, triple library preparations were performed and pooled for each sample, and still minimal amplicons were generated after 30 cycles of PCR.…”

“…The conclusion of the study was that, although murine fetuses do not appear to be populated by microbial communities, they are exposed to bacterial DNA in utero . Conversely, in a subsequent molecular study by Kuperman et al (18), 24 murine placental samples (four regions were sampled from two placentas each from three mice at gestational day 19) had no detectable 16S rRNA gene amplicons after PCR. Hence, more comprehensive investigations were needed.…”

The Dual Role of HLA-C in Tolerance and Immunity at the Maternal-Fetal Interface

“…Although pregnant women can generate protective immune responses to a variety of pathogens, when infections occur during pregnancy, they can cause severe maternal and fetal morbidity (98)(99)(100)(101). Human placenta has no microbiome, but many pathogens infect the placenta before transmission to the fetus occurs (102,103). Pathogens that can directly infect trophoblasts and other placental cells, include but are not limited to: Human Cytomegalovirus (HCMV), Hepatitis C virus (HCV), Herpes Simplex virus (HSV), Human Papillomavirus (HPV), Zika Virus (ZIKV), Rubella Virus, Varicella Zoster Virus (VZV), parvovirus B19, Listeria Monocytogenes (L. monocytogenes), Toxoplasma gondii, Ureaplasma urealyticum, Mycoplasma hominis (100, [104][105][106][107][108][109][110][111].…”

No Consistent Evidence for Microbiota in Murine Placental and Fetal Tissues

“…The conclusion of the study was that, although murine fetuses do not appear to be populated by microbial communities, they are exposed to bacterial DNA in utero. Conversely, in a subsequent molecular study by Kuperman et al (18), 24 murine placental samples (four regions were sampled from two placentas each from three mice at gestational day 19) had no detectable 16S rRNA gene amplicons after PCR. Hence, more comprehensive investigations were needed.…”