The Vaginal Microbiome as a Tool to Predict rASRM Stage of Disease in Endometriosis: a Pilot Study Original paper

What Was Studied?

This pilot observational cross-sectional study investigated the vaginal and gut microbiome profiles in women with and without endometriosis to evaluate their potential as less invasive diagnostic tools for the disease. Researchers analyzed microbiome samples collected during two menstrual cycle phases—follicular and menstrual—from 35 women with endometriosis and 24 controls. They further explored the microbiome’s association with disease severity, categorized by rASRM (revised American Society for Reproductive Medicine) stages, using 16S rRNA sequencing and machine learning models.

Who Was Studied?

The study included 59 women aged 21–49, with 35 participants having surgically confirmed endometriosis and 24 serving as controls. Participants were excluded if they had a history of autoimmune diseases, active infections, or recent use of antibiotics or hormones. Vaginal and rectal samples were obtained from all subjects to evaluate microbial community state types (CSTs) and their variability across menstrual phases.

What Were the Most Important Findings?

The study highlighted significant shifts in vaginal microbiome profiles between the follicular and menstrual phases, particularly in the distribution of community state types (CSTs). During menstruation, CST IV, defined by increased anaerobic bacterial diversity, became more prominent, while CSTs II and V, dominated by Lactobacillus gasseri and Lactobacillus jensenii, respectively, disappeared. Notably, Lactobacillus crispatus was more abundant in endometriosis patients during menstruation, even within the inflammatory environment. This finding suggests a potential immunomodulatory role for L. crispatus, likely tied to its production of lactic acid, which lowers vaginal pH, inhibits pathogenic bacterial growth, and promotes immune homeostasis. By fostering an anti-inflammatory phenotype through the stimulation of cytokines like IL-10 and regulatory immune cells, L. crispatus may help counterbalance the inflammatory state characteristic of endometriosis.

Moreover, the vaginal microbiome during menstruation demonstrated predictive value for endometriosis severity. Specifically, an operational taxonomic unit (OTU) from the genus Anaerococcus strongly correlated with advanced rASRM stages (3–4), marking its potential as a biomarker for disease progression. These findings underscore the diagnostic and therapeutic promise of the vaginal microbiome, particularly L. crispatus and its role in immune modulation. Future research should further investigate these microbial associations, their lactic acid production, and their influence on the immunological environment in endometriosis.

What Are the Greatest Implications of This Study?

This study provides a foundation for using the vaginal microbiome as a non-invasive diagnostic tool for assessing endometriosis severity. The identification of Anaerococcus as a biomarker for disease stage highlights a significant advancement in linking microbiome alterations to gynecological pathology. Additionally, the potential involvement of Lactobacillus crispatus in modulating local immune responses suggests a dual diagnostic and therapeutic role for microbiome-targeted interventions. However, the findings need validation in larger cohorts due to its pilot nature and small sample size.