Vaginal swab preprocessing
Vaginal swabs collection was performed by two gynecologists following a strict sampling protocol. In brief, the participants assumed a lithotomy position and the gynecologist used a sterile swab to press against the posterior fornix after a sterile speculum was inserted into the vagina. After sampling, the swab head with vaginal discharge was immediately cut using a sterile surgical scissor and placed in a sterile tube. The sample was then placed in dry ice and transferred to a -80°C freezer within 6 hours for subsequent 16S rRNA gene sequencing.