Comparison of microbial profiles and viral status along the vagina-cervix-endometrium continuum of infertile patients

For decades, the endometrium was considered to be a sterile environment. However, now this concept is disputed, and there is growing evidence that microbiota composition might affect endometrial receptivity. Routine clinical management of infertility is still limited to a microbiological assessment of the lower reproductive tract. The purpose of this study was to compare the abundance of various bacterial, fungal, and viral species, qualitatively and quantitatively, in vaginal, cervical, and endometrial biomaterial of infertile patients. A total of 300 samples from 100 infertile patients of a private assisted reproduction clinic were analyzed. A broad real-time polymerase chain reaction panel was used to identify 28 relevant microbial taxa as well as three members of the Herpesviridae family. All patients underwent endometrial biopsy for further histopathological evaluation. Analysis of the microbial diversity (within the boundaries of the detection panel) revealed that Shannon indexes in the cervix and vagina were similar (1.4 × 10⁻² (1.6 × 10⁻³ – 6.5 × 10⁻¹) vs 1.9 × 10⁻² (2.3 × 10⁻³ – 5.3 × 10⁻¹), respectively, <i>p</i> = 0.502), whereas endometrial indexes differed significantly from both regions (0 (0 – 1.4 × 10⁻¹), <i>p</i> &lt; 0.0001). Surprisingly, 17 microbial and viral taxa were detected in at least one sample. Endometrium exhibited a quite distinct microbiological profile, being different at the detection rates of 14 taxa (<i>p</i> &lt; 0.05). Remarkably, 4% and 2% of endometrial samples were positive for Cytomegalovirus and <i>Candida spp.</i>, respectively, while these were undetectable in corresponding cervical and vaginal samples. Prevalence of the <i>Gardnerella vaginalis</i> + <i>Prevotella bivia</i> + <i>Porphyromonas spp.</i> group in endometrium was associated with a low abundance of <i>Lactobacillus spp</i>. (<i>p</i> = 0.039). No noteworthy associations were identified between various microbiota characteristics and clinical parameters, such as chronic endometritis, uterine polyps and adhesions, endometriosis, and a history of sexually transmitted infections. These findings indicate that the microbiological profile of the endometrium is unique, and the analysis of the lower reproductive tract should supplement, rather than be a substitute for it.

数十年来，子宫内膜一直被认为是无菌环境。然而，如今这一观点已受到广泛质疑，越来越多的证据表明微生物群组成可能影响子宫内膜容受性。当前不孕的临床常规管理仍局限于下生殖道的微生物学评估。本研究旨在对不孕患者的阴道、宫颈及子宫内膜生物样本中的各类细菌、真菌和病毒物种进行定性与定量的丰度比较。

本研究共分析了某私立辅助生殖诊所100名不孕患者的300份样本。研究采用广谱实时聚合酶链反应（real-time polymerase chain reaction）检测组合，对28种相关微生物类群以及疱疹病毒科（Herpesviridae）的3个成员进行鉴定。所有患者均接受子宫内膜活检，以开展进一步的组织病理学评估。

在本检测组合的覆盖范围内对微生物多样性进行分析后发现，宫颈与阴道的香农指数（Shannon index）相近（分别为1.4×10⁻² [1.6×10⁻³ – 6.5×10⁻¹] 与1.9×10⁻² [2.3×10⁻³ – 5.3×10⁻¹]，p=0.502），而子宫内膜的香农指数与这两个区域均存在显著差异（0 [0 – 1.4×10⁻¹]，p<0.0001）。

令人意外的是，至少在1份样本中检测到了17种微生物与病毒类群。子宫内膜展现出截然不同的微生物学特征，在14个类群的检出率上存在显著差异（p<0.05）。值得注意的是，4%与2%的子宫内膜样本分别呈巨细胞病毒（Cytomegalovirus）阳性与假丝酵母菌属（Candida spp.）阳性，而对应的宫颈及阴道样本中未检出上述病原体。阴道加德纳菌（Gardnerella vaginalis）+ 普雷沃菌（Prevotella bivia）+ 卟啉单胞菌属（Porphyromonas spp.）组合在子宫内膜中的检出情况与乳杆菌属（Lactobacillus spp.）的低丰度存在显著关联（p=0.039）。

本研究未发现各类微生物群特征与慢性子宫内膜炎、子宫息肉与粘连、子宫内膜异位症以及性传播感染病史等临床参数之间存在显著关联。

上述研究结果表明，子宫内膜的微生物学特征具有独特性，对下生殖道的微生物学分析仅可作为补充手段，而非子宫内膜相关检测的替代方案。