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The Uterine Microbiota
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Jonah Bardos, Carlos Simón, Inmaculada Moreno
Over the past five years, there has been a new focus on analyzing the uterine microbiome after a pilot study in 2016 showed that women with a pathogenic (defined as non-Lactobacillus dominated, NLD) uterine environment had an almost 40% decrease in pregnancy rates.4 Another study in 2017 utilized targeted sequencing and microarray data focused on the hypervariable regions of 16S rRNA and showed that the uterine microbiome at the time of embryo transfer during IVF can be characterized by sequencing the tip of the transfer catheter from the embryo transfer.5 Since then, many authors have been attempting to characterize the natural microbiome of the uterus to determine what effect the uterine microbiome has on pregnancy outcomes.6 Studies have shown conflicting results regarding the “normal” uterine microbiome; however, it does appear that Lactobacillus is consistently present among the physiological endometrial microbiome.7
A transcriptomic insight into the human sperm microbiome through next-generation sequencing
Published in Systems Biology in Reproductive Medicine, 2023
Celia Corral-Vazquez, Joan Blanco, Riccardo Aiese Cigliano, Sarrate Zaida, Francesca Vidal, Ester Anton
Concerning the reproductive system, an association between their microbiome composition and human fertility has been stablished by some authors. Studies in women have revealed certain consistencies in the vaginal microbiome, being Lactobacillus the predominant bacterial genus (Mändar et al. 2015). Imbalances in this vaginal and uterine microbiome are associated with adverse pregnancy outcomes, infertility treatment failure, and irregular endometrial function (Koedooder et al. 2019). In men, specific microbiota has been detected in the genital tract (Koedooder et al. 2019). Further, studies focused on the seminal microbiome have revealed a relation between the microbiome composition and seminal quality, acrosome reaction and sperm DNA fragmentation. While the abundance of bacterial genus like Lactobacillus or Gardnerella show an association with fertility and good quality semen, others like Anaerococcus, Prevotella, Neisseria, Klebsiella, and Pseudomonas have been associated with infertility and seminal impairments (Hou et al. 2013; Liu et al. 2014; Weng et al. 2014; Mändar et al. 2017; Chen et al. 2018; Monteiro et al. 2018; Baud et al. 2019; Koedooder et al. 2019). Intriguingly, some authors have revealed that couples exhibit some kind of complementation between the semen and vagina microbiota (Mändar et al. 2015; Mändar et al. 2018).
The early life education of the immune system: Moms, microbes and (missed) opportunities
Published in Gut Microbes, 2020
The maternal microbiota in the gut and reproductive tract undergoes significant changes during pregnancy that is influenced by a combination of hormonal, metabolic, and immunological factors as well as by maternal diet, supplement intake, and antibiotics use.28 Alterations in the vaginal microbiota have been linked to preterm birth, a major cause of worldwide neonatal morbidity and mortality.29 Activation of maternal immunity leading to preterm birth has been well documented;30 however, an impact on the developing fetal immune system and subsequent long-term health consequences in offspring cannot be ruled out. Maternal gut microbes metabolize dietary components that is passed to the developing fetus across the placenta. The placenta is the highly adapted primary interface between the mother and the developing fetus that facilitates the exchange of nutrients, gases, xenobiotics, and waste products while protecting the fetus from rejection by the maternal immune system. It is also the focus of a controversial and debated topic about the existence of an intra-uterine microbiome in a healthy pregnancy. The long-held premise that the fetus develops in a sterile environment in utero is being challenged.31 Some studies have demonstrated the presence of low abundance commensal bacteria in the healthy placenta,32,33 while others refute this premise of a placental microbiome.34,35 Distinct bacterial profiles were also reported in gestational week 20 fetal intestines, findings that need to be corroborated in other independent cohorts.36 While exposure of the fetus to live bacteria in utero remains to be confirmed, the fetal tissues are likely exposed to numerous microbial metabolites and microbial fragments of maternal origin that are transferred across the placenta from the maternal serum. Gut microbes can induce an IgG antibody response in hosts that protect from systemic infections.37 Importantly, these commensal-specific IgG antibodies can be transferred across the placenta to the offspring where they regulate mucosal CD4+T cell responses to commensal antigens early after birth.38 Maternal IgG antibodies can also facilitate transfer of bacterial compounds themselves across the placenta.39 In a mouse model where bacteria were only present during pregnancy, maternal antibodies enhanced transfer of bacterial compounds, including ligands for the aryl hydrocarbon receptor (AhR), from the mother to the offspring where they primed the developing immune system. Maternal enteric microbes also ferment dietary fibers to the short-chain fatty acid (SCFA) acetate, that suppresses allergic airway disease, a mouse model for human asthma, by enhancing Treg cell numbers and function in adult offspring.40 In the context of a maternal infection, bacterial peptidoglycan, which is a ligand for Toll-like Receptor 2 (TLR2), traversed the placenta to influence fetal neuro-proliferation.41 Passage of other microbial TLR ligands across the placenta that influence fetal immune development remains a formal possibility.