An Analysis of the Digestive and Reproductive Tract Microbiota in Infertile Women with Obesity

Abstract

Previous studies have linked the microbiome of distinct body habitats to obesity and infertility; however, the often-divergent results observed have left the role of the so-called "second genome" in obese infertile patients incompletely explored. Here, we present a prospective observational multicenter study of oral, gut, endometrial, and vaginal microbiota of infertile patients classified according to BMI. Patients collected saliva/fecal samples, while vaginal/endometrial fluid samples were collected in the clinic. Total bacterial DNA was extracted, and microbiota profiles were analyzed by 16S rRNA gene sequencing. Our results showed no differences in the Bacteroidetes/Firmicutes ratio (proposed obesity hallmark) in the gut microbiota between patients with obesity and normal weight; however, a tendency for higher levels of genera such as Escherichia-Shigella in normal-weight patients was observed; in comparison, patients with obesity possessed increased numbers of Parasutterella and Roseburia. In the reproductive tract, vaginal samples possessed a similar microbiota to endometrial fluid, both largely colonised by Lactobacillus, Gardnerella, and Streptococcus, supporting the hypothesis that uterine colonisation proceeds from vaginal bacteria ascension. Additionally, higher prevalence of a Streptococcus-dominated (>50%) endometrial microbiota was observed among patients with obesity. This first description of the human digestive and reproductive tract microbiota in infertile women with obesity may explain their poor reproductive outcomes.

Keywords: Streptococcus; endometrium; female infertility; gut microbiota; obesity; reproductive tract microbiota.

Figure 1

Schematic view of collected samples. Eighty-three patients from four centres were placed in four groups according to BMI values. A total of 327 samples of saliva, faeces, endometrial fluid, and vaginal swabs were used to describe the human digestive and reproductive tract microbiota in infertile patients with obesity and to assess any relationship between the microbiota and obesity.

Figure 2

Alpha and beta diversities of the human microbiota in infertile patients with normal weight and obesity. (A) Alpha diversity (Shannon index) of body habitats. Comparisons between sample types were performed using Kruskal–Wallis, and two-by-two comparisons were performed using the Dunn test. (B) Principal component analysis (PCA) plot of beta diversity after PERMANOVA test for both general and two-by-two comparisons. *** p < 0.001.

Figure 3

Microbiota composition of the oral cavity in infertile patients with normal weight and obesity. (A) Differences in alpha diversity (Species Richness, Shannon, and Phylogenetic Diversity indexes) was analysed using the ANOVA test. (B) Principal component analysis (PCA) of beta diversity after PERMANOVA analysis. (C,D) Microbiota structure of saliva samples at the (C) phylum and (D) genus levels. Normal weight (BMI: 18.5–29.9 Kg/m²), Obesity I (BMI: 30–34.9 Kg/m²), Obesity II (BMI: 35–39.9 Kg/m²), Obesity III (BMI ≥ 40 Kg/m²).

Figure 4

Microbiota compositions of the gut in infertile patients with normal weight and obesity. (A) Differences in alpha diversity (Species Richness, Shannon, and Phylogenetic Diversity indexes) were analysed using the ANOVA test. (B) Principal component analysis (PCA) of beta diversity after PERMANOVA analysis. (C,D) Microbiota structure of faecal samples at the (C) phylum and (D) genus levels. (E–G) Differential abundance of faecal taxa in normal weight patients and patients with obesity: (E) relative abundance of Escherichia-Shigella, (F) relative abundance of Parasutterella, and (G) relative abundance and percentage of patients with the presence of Roseburia. (H,I) Bacteroidetes/Firmicutes relative abundance (H) and ratio (I) in patients classified according to BMI values. Comparisons assessed by ANOVA test. Normal weight (BMI: 18.5–29.9 Kg/m²), Obesity I (BMI: 30–34.9 Kg/m²), Obesity II (BMI: 35–39.9 Kg/m²), Obesity III (BMI ≥ 40 Kg/m²).

Figure 5

Microbiota composition of the reproductive tract. Analysis of endometrial fluid (A,C,E,G,I) and vaginal aspirate (B,D,F,H,J) samples in infertile patients with normal weight and obesity. (A,B) Differences in alpha diversity (Species Richness, Shannon, and Phylogenetic Diversity indexes) were analysed using the ANOVA test. (C,D) Principal component analysis (PCA) of beta diversity after PERMANOVA analysis. (E–H) Microbiota structure of endometrial fluid and vaginal aspirate samples at the (E,F) phylum and (G,H) genus levels. (I,J) Percentage of patients with (I) presence (>1%) and (J) dominance (>50%) of Streptococcus in endometrial fluid and vaginal aspirate samples in each study group. Normal weight (BMI: 18.5–29.9 Kg/m²), Obesity I (BMI: 30–34.9 Kg/m²), Obesity II (BMI: 35–39.9 Kg/m²), Obesity III (BMI ≥ 40 Kg/m²).

Figure 6

Comparison of microbiota composition between all body habitats. Relative abundance (size) of taxa in the microbiota of infertile patients with obesity in saliva, faeces, endometrial fluid, and vaginal samples. Data for infertile patients with normal weight (Nw) and obesity (Ob-I, Ob-II, Ob-III).