The Composition of Placental Microbiota and Its Association With Adverse Pregnancy Outcomes

Comparative analysis of oral, placental, and gut microbiota characteristics, functional features and microbial networks in healthy pregnant women

AIM

Most studies on pregnant women focus on analyzing individual microbial species at specific body sites. This study aims to explore the characteristics, functions, and microbial networks of the oral, placental, and gut microbiota in healthy pregnant women.

METHODS

A total of 23 healthy pregnant women were enrolled in this study. We analyzed the microbial composition, functional profiles, and microbial networks of the oral, placental, and gut microbiota using 16S rRNA gene sequencing.

RESULTS

Our findings revealed significant differences in microbial composition across these three sites. The placental microbiota contained a relatively high proportion of low-abundance microorganisms, which were more diverse and evenly distributed compared to the gut and oral microbiota. The microbial composition at each site displayed distinct characteristics, likely influenced by environmental, physiological, and biological factors. The placental microbiota exhibited a complex network of tightly interconnected genera, whereas the gut microbiota showed sparser connections, with fewer closely related genera compared to the placental and oral microbiota. Functional differences were also observed among the three microbiota, with each playing a unique role in maintaining host health and metabolic balance. While the oral and gut microbiota shared functional similarities, the placental microbiota exhibited distinct functional characteristics.

CONCLUSIONS

This study provides valuable insights into the microbial communities of healthy pregnant women, offering important data for microbiological research during pregnancy and laying the foundation for future investigations into the roles of these microbial communities in maternal health.

Assessment of the placental microbiota of preterm infants with pneumonia: a case control study

Objective

To investigate the specific characteristics and differences in the placental microbiome of preterm infants with and without pneumonia.

Methods

Fifty-nine infants born at 32-36 weeks' gestation were enrolled in this study. Among them, 33 developed pneumonia within 48 hours of birth, while the remaining 26 did not. Placental swabs were collected at birth for DNA extraction, from which the placental microbial composition was analyzed using a bioinformatics pipeline following PCR amplification of genetic material and subsequent sequencing of bacterial 16S rRNA.

Results

Significant differences in both the alpha and beta diversities were found between the two groups (P<0.05). Proteobacteria, Firmicutes, and Actinobacteriota were identified as the predominant phyla in the placenta, while predominant identified genera included Brevundimonas, Caulobacter, Lactobacillus, and Citrobacter. There were no significant inter-group differences in the relative abundances of the predominant phyla and genera except Lactobacillus(P>0.05). Compared to infants without pneumonia, those with pneumonia demonstrated a decreased abundance of Lactobacillus, and an increased abundance of Ureaplasma and Staphylococcus (P<0.05). The relative abundance of Ureaplasma was positively correlated with that of Staphylococcus, and negatively correlation with that of Lactobacillus (P<0.05). Notably, we observed significant disparities in the metabolic pathways and phenotypes between the two groups (P<0.05).

Conclusion

Overall, this study suggests that alterations in the placental microbiome may be linked to the onset of pneumonia in preterm infants. Further investigations are required to elucidate the relationship between microbiota and disease pathogenesis.

Unveiling the placental bacterial microbiota: implications for maternal and infant health

The human placenta is a unique organ that forms under specific physiological conditions and plays a crucial role in nutrient and metabolite exchange between the mother and fetus. Research on the placenta is important for understanding maternal-fetal diseases. Traditionally, the placenta was considered "sterile," but advancements in detection techniques have revealed the presence of a low level of microorganisms. This discovery challenges the traditional notion that the uterine placenta is sterile. The revelation of this truth marks a significant breakthrough in medical research, prompting more researchers to focus on this vital organ, the placenta. Placental microbial communities may originate from the oral, vaginal, and intestinal microbiota of expectant mothers. These microorganisms may reach the maternal-fetal interface, collectively shaping the placental microbiota and contributing to the composition of normal placental microbial communities. Abnormal placental microbial communities may be associated with some pregnancy complications and fetal developmental issues such as preterm birth, gestational hypertension, fetal growth restriction, and gestational diabetes mellitus. Intervention strategies targeting microbial communities, which include modulation of placental microbiota composition or function, such as probiotics, may help prevent or treat complications related to abnormal placental microbiota during pregnancy.

Exploring the composition of placental microbiome and its potential origin in preterm birth

Introduction

For years, the placenta was believed to be sterile, but recent studies reveal it hosts a unique microbiome. Despite these findings, significant questions remain about the origins of the placental microbiome and its effects on pregnancy and fetal health. Some studies suggest it may originate from the vaginal tract, while others indicate that oral bacteria can enter the maternal bloodstream and seed the placenta. However, research analyzing the vaginal, oral, and placental microbiomes within the same cohort is lacking. Additionally, it's unclear whether the placental microbiome differs between healthy pregnancies and those with complications like preterm birth (PTB), which remains a leading cause of neonatal morbidity and mortality worldwide.

Methods

In this study, we performed 16S rRNA gene sequencing to investigate the composition of the oral and placental microbiome in samples collected from 18 women who experienced PTB and 36 matched controls who delivered at term (TB), all of whom were part of the Molecular Signature in Pregnancy (MSP) study. We leveraged on the multisite microbiome sampling from the MSP participants and on our previously published vaginal microbiome data to investigate the potential origins of the placental microbiome and assess whether its composition varies between healthy and complicated pregnancies.

Results and Discussion

Our analysis revealed distinct profiles in the oral microbiome of PTB subjects compared to those who delivered at term. Specifically, we observed an increased abundance of Treponema maltophilum, Bacteroides sp, Mollicutes, Prevotella buccae, Leptotrichia, Prevotella_sp_Alloprevotella, in the PTB group. Importantly, Treponema maltophilum species showed higher abundance in the PTB group during the second trimester, suggesting its potential use as biomarkers. When we assessed the placenta microbiome composition, we found that Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were the most dominant phyla. Interestingly, microorganisms such as Ureaplasma urealyticum were more abundant in PTB placenta samples. Our findings suggest that the placenta microbiome could originate from the oral or vaginal cavities, with a notable increase in the crosstalk between the vaginal and placental sites in cases of PTB. Specifically, our data revealed that in PTB cases, the placental microbiome exhibited a closer resemblance to the vaginal microbiome, whereas in term pregnancies, the placental microbiome was similar to the oral microbiome.

Gut microbiome and Alzheimer's disease: What we know and what remains to be explored

With advancement in human microbiome research, an increasing number of scientific evidences have endorsed the key role of gut microbiota in the pathogenesis of Alzheimer disease. Microbiome dysbiosis, characterized by altered diversity and composition, as well as rise of pathobionts influence not only various gut disorder but also central nervous system disorders such as AD. On the basis of accumulated evidences of past few years now it is quite clear that the gut microbiota can control the functions of the central nervous system (CNS) through the gut-brain axis, which provides a new prospective into the interactions between the gut and brain. The main focus of this review is on the molecular mechanism of the crosstalk between the gut microbiota and the brain through the gut-brain axis, and on the onset and development of neurological disorders triggered by the dysbiosis of gut microbiota. Due to microbiota dysbiosis the permeability of the gut and blood brain barrier is increased which may mediate or affect AD. Along with this, bacterial population of the gut microbiota can secrete amyloid proteins and lipopolysaccharides in a large quantity which may create a disturbance in the signaling pathways and the formation of proinflammatory cytokines associated with the pathogenesis of AD. These topics are followed by a critical analysis of potential intervention strategies targeting gut microbiota dysbiosis, including the use of probiotics, prebiotics, metabolites, diets and fecal microbiota transplantation. The main purpose of this review includes the summarization and discussion on the recent finding that may explain the role of the gut microbiota in the development of AD. Understanding of these fundamental mechanisms may provide a new insight into the novel therapeutic strategies for AD.

The importance of gut microbiome in the perinatal period

This narrative review describes the settlement of the neonatal microbiome during the perinatal period and its importance on human health in the long term. Delivery methods, maternal diet, antibiotic exposure, feeding practices, and early infant contact significantly shape microbial colonization, influencing the infant's immune system, metabolism, and neurodevelopment. By summarizing two decades of research, this review highlights the microbiome's role in disease predisposition and explores interventions like maternal vaginal seeding and probiotic and prebiotic supplementation that may influence microbiome development.

CONCLUSION

The perinatal period is a pivotal phase for the formation and growth of the neonatal microbiome, profoundly impacting long-term health outcomes.

WHAT IS KNOWN

• The perinatal period is a critical phase for the development of the neonatal microbiome, with factors such as mode of delivery, maternal diet, antibiotic exposure, and feeding practices influencing its composition and diversity, which has significant implications for long-term health. • The neonatal microbiome plays a vital role in shaping the immune system, metabolism, and neurodevelopment of infants.

WHAT IS NEW

• Recent studies have highlighted the potential of targeted interventions, such as probiotic and prebiotic supplementation, and innovative practices like maternal vaginal seeding, to optimize microbiome development during the perinatal period. • Emerging evidence suggests that specific bacterial genera and species within the neonatal microbiome are associated with reduced risks of developing chronic conditions, indicating new avenues for promoting long-term health starting from early life.

Evaluation of the Human Placental Microbiota in Early- and Late-Onset Pre-Eclampsia

INTRODUCTION

Despite many decades of research, the exact etiology of pre-eclampsia (PE) remains unknown. Several etiopathologies have been suggested, including the role of the placental microbiota. However, the existence of placental microbiota and its possible contribution to pregnancy complications, particularly PE has remained controversial.

AIM

The present study was designed to identify different microbes that co-exist the placenta of women with early- and late-onset PE.

METHODS

Thirty age-matched normotensive and early-onset as well as age-matched normotensive and late-onset pre-eclamptic women respectively, were recruited. After obtaining an informed consent, the placental tissues were obtained through caesarian section with sterile and standardized clinical procedures. DNA was extracted from each tissue and microbiome analysis was conducted using a targeted 16 S analysis and the reads were analyzed with bioinformatics.

RESULTS

There was a significance difference between the blood pressure of early-/late-onset PE compared with age-matched normotensive controls, respectively. In addition, the reads from placencental samples were classified as belonging to the phyla, Actinobacteria, Firmicutes, Bacteroidetes, Proteobacteria, with Proteobacteria dominated by the classes Pseudomonadales and Gammaproteobacteria with smaller amounts of Actinobacteria and Bacteroidetes. There was no significant difference between the placental bacterial species of early-/late-onset PE compared with age-matched normotensive controls, respectively. Further analysis found no correlation between bacterial species and early- or late-onset PE.

CONCLUSION

The present results demonstrate a low biomass of bacterial species, which might further indicate that the placental samples had very low levels of bacteria species and there is no correlation between the bacterial composition and early- or late-onset PE.

The Existence of an Intra-Amniotic Microbiome: Assessing a Controversy

The existence of intra-amniotic and placental microbiomes during pregnancy has been the source of considerable debate, with research yielding conflicting evidence. This study evaluated investigations into the putative presence of these microbiomes in healthy pregnancies by identifying design and data interpretation issues, particularly concerning contamination in samples with low-density bacterial DNA. Positive findings from diverse populations suggest a consistent presence of microbiota in the intra-amniotic space. Negative conclusions regarding the existence of these prenatal microbiomes emphasise the impact of contamination in the analysis of samples with low-density bacterial DNA. This study concluded that there is no definitive evidence to refute the existence of intra-amniotic microbiomes in healthy pregnancies. Also, it provides suggestions for controlling potential contamination factors in future research on intra-amniotic and placental microbial populations.

Intestinal flora and pregnancy complications: Current insights and future prospects

Numerous studies have demonstrated the pivotal roles of intestinal microbiota in many physiopathological processes through complex interactions with the host. As a unique period in a woman's lifespan, pregnancy is characterized by changes in hormones, immunity, and metabolism. The gut microbiota also changes during this period and plays a crucial role in maintaining a healthy pregnancy. Consequently, anomalies in the composition and function of the gut microbiota, namely, gut microbiota dysbiosis, can predispose individuals to various pregnancy complications, posing substantial risks to both maternal and neonatal health. However, there are still many controversies in this field, such as "sterile womb" versus "in utero colonization." Therefore, a thorough understanding of the roles and mechanisms of gut microbiota in pregnancy and its complications is essential to safeguard the health of both mother and child. This review provides a comprehensive overview of the changes in gut microbiota during pregnancy, its abnormalities in common pregnancy complications, and potential etiological implications. It also explores the potential of gut microbiota in diagnosing and treating pregnancy complications and examines the possibility of gut-derived bacteria residing in the uterus/placenta. Our aim is to expand knowledge in maternal and infant health from the gut microbiota perspective, aiding in developing new preventive and therapeutic strategies for pregnancy complications based on intestinal microecology.

The influence of placenta microbiota of normal term pregnant women on immune regulation during pregnancy

BACKGROUND

The concerted regulation of placenta microbiota and the immune responses secures the occurrence and development of pregnancy, while few studies reported this correlation. This study aimed to explore the relationship between the placenta microbiota and immune regulation during pregnancy.

METHODS

Twenty-six healthy pregnant women scheduled for elective cesarean section in the First Affiliated Hospital of Jinan University who met the inclusion criteria were recruited. Placenta and peripheral venous blood samples were collected. Microbiota in placental tissue was detected using high-throughput sequencing. Flow cytometry was used to detect immune cells in placental tissue and peripheral venous blood. ELISA and Luminex liquid chip technology were used to detect the content of cytokines in placental tissue and peripheral venous blood, respectively.

RESULTS

The placental microbiota has stimulating effects on the local immunity of the placenta and mainly stimulates the placental balance ratio CD56 + CD16 + /CD56 + CD16 and the placental macrophages, that is, it plays the role of immune protection and supporting nutrition. The stimulating effect of placental microbiota on maternal systemic immunity mainly induces peripheral Treg cells and B lymphocytes.

CONCLUSION

The placental microbiota may be an important factor mediating local immune regulation in the placenta, and placental microbiota participates in the regulatory function of the maternal immune system.

Might Gut Microbiota Be a Target for a Personalized Therapeutic Approach in Patients Affected by Atherosclerosis Disease?

In recent years, the increasing number of studies on the relationship between the gut microbiota and atherosclerosis have led to significant interest in this subject. The gut microbiota, its metabolites (metabolome), such as TMAO, and gut dysbiosis play an important role in the development of atherosclerosis. Furthermore, inflammation, originating from the intestinal tract, adds yet another mechanism by which the human ecosystem is disrupted, resulting in the manifestation of metabolic diseases and, by extension, cardiovascular diseases. The scientific community must understand and elucidate these mechanisms in depth, to gain a better understanding of the relationship between atherosclerosis and the gut microbiome and to promote the development of new therapeutic targets in the coming years. This review aims to present the knowledge acquired so far, to trigger others to further investigate this intriguing topic.

Microbial Profiling of Amniotic Fluid, Umbilical Blood and Placenta of the Foaling Mare

The presence of a microbiome/microbiota in the placenta is hotly debated. In previous studies, the presence of bacteria in equine amniotic fluid and umbilical blood was independent of foal health. The objective of the present study was to determine if the same bacteria are present in the equine placenta as in amniotic fluid and umbilical blood. Samples were obtained from 24 parturient mares and foals. Placental bacterial DNA was extracted, and the microbiome was identified using 16S rRNA sequencing. All amniotic fluid samples contained some polymorphonucleocytes; bacteria were isolated from four samples. Aerobic or anaerobic growth was found in 18 and 3 umbilical blood samples, respectively. Serum amyloid A was <5 mg/L in all 24 samples, total WBC varied between 2900 and 10,700/µL, and fibrinogen varied between 0 and 5.16 g/L. In jugular blood, serum amyloid A was <5 mg/L in all 24 foals, total white blood count was 3200 to 8100/µL, and fibrinogen was 0.44 to 4.42 g/L. The diversity of bacterial microbiota was similar in all placental regions at the phylum level but differed at the genus level; the most abundant phyla were Proteobacteria (42-46.26%) and Actinobacteria (26.91-29.96%). In conclusion, bacteria were found in the fetal compartments and placenta of healthy equine pregnancies; however, we can neither prove nor disprove the hypothesis that the placenta has its own microbiome.

Alterations in the Gut Microbiome and Metabolisms in Pregnancies with Fetal Growth Restriction

Fetuses diagnosed with fetal growth restriction (FGR) are at an elevated risk of stillbirth and adulthood morbidity. Gut dysbiosis has emerged as one of the impacts of placental insufficiency, which is the main cause of FGR. This study aimed to characterize the relationships among the intestinal microbiome, metabolites, and FGR. Characterization was conducted on the gut microbiome, fecal metabolome, and human phenotypes in a cohort of 35 patients with FGR and 35 normal pregnancies (NP). The serum metabolome was analyzed in 19 patients with FGR and 31 normal pregnant women. Multidimensional data was integrated to reveal the links between data sets. A fecal microbiota transplantation mouse model was used to determine the effects of the intestinal microbiome on fetal growth and placental phenotypes. The diversity and composition of the gut microbiota were altered in patients with FGR. A group of microbial species altered in FGR closely correlated with fetal measurements and maternal clinical variables. Fecal and serum metabolism profiles were distinct in FGR patients compared to those in the NP group. Altered metabolites were identified and associated with clinical phenotypes. Integrated multi-omics analysis revealed the interactions among gut microbiota, metabolites, and clinical measurements. Microbiota from FGR gravida transplanted to mice progestationally induced FGR and placental dysfunction, including impaired spiral artery remodeling and insufficient trophoblast cell invasion. Taken together, the integration of microbiome and metabolite profiles from the human cohort indicates that patients with FGR endure gut dysbiosis and metabolic disorders, which contribute to disease pathogenesis. IMPORTANCE Downstream of the primary cause of fetal growth restriction are placental insufficiency and fetal malnutrition. Gut microbiota and metabolites appear to play an important role in the progression of gestation, while dysbiosis induces maternal and fetal complications. Our study elaborates the significant differences in microbiota profiles and metabolome characteristics between women with FGR and normal pregnancies. This is the first attempt so far that reveals the mechanistic links in multi-omics in FGR, providing a novel insight into host-microbe interaction in placenta-derived diseases.