<i>Lactobacillus gasseri</i> CECT 30648 shows probiotic characteristics and colonizes the vagina of healthy women after oral administration

Vaginal dysbiosis is linked to recurrent infections and reproductive complications. Probiotics may restore vaginal microbiota, but there is modest evidence to support vaginal colonization after oral administration. This work aimed to screen a vaginal lactobacilli collection (<i>n</i> = 45) and assess vaginal colonization of selected candidates. <i>Lactobacillus gasseri</i> CECT 30648 (Lg) and <i>Lactobacillus crispatus</i> CECT 30647 (Lc) showed excellent <i>in vitro</i> attributes, including antagonism against 10 urogenital pathogens, resistance to gastrointestinal tract and vaginal environment-including high concentrations of biogenic amines-and adhesion to vaginal epithelium. Forty-eight healthy women (18-45 years old) were randomly allocated to consume daily a capsule containing Lg (10⁹ CFU), a combination of Lg plus Lc (1.5 × 10⁹ CFU), or placebo for up to 18 days (between menses). Volunteers collected vaginal samples every 3 days. The primary endpoint was the presence of probiotic strains in vaginal swabs confirmed by strain-specific quantitative PCR. Secondary variables included vaginal microbiota composition and tolerability, among others. Probiotics were well tolerated. Lg but not Lc was detected in 55.9% of participants in active groups (9 in Lg and 10 in Lg + Lc) throughout the study (<i>P</i> = 0.005 aggregated probiotic groups vs placebo). The sum of relative abundances of non-lactobacilli genera was significantly reduced in the probiotic group after intervention (<i>P</i> = 0.047 vs day 0), and there was a positive transition toward lactobacilli-dominated community state types (<i>P</i> = 0.039 vs day 0). Overall, we show that <i>L. gasseri</i> CECT 30648 exerts a broad-spectrum antimicrobial activity and can colonize the vaginal tract of healthy women, thus showing potential to promote vaginal health. The trial was registered in clinicaltrials.gov (NCT05688397).IMPORTANCEThe use of probiotics to promote vaginal health is increasing because vaginal dysbiosis has been linked to numerous gynecological and reproductive complications. While vaginal administration of probiotics using devices or creams has been widely investigated, there is limited evidence supporting vaginal colonization of a probiotic administered orally. It is therefore imperative to perform extensive <i>in vitro</i> characterization to select a vaginal probiotic that can survive the gastrointestinal transit and effectively colonize the vaginal tract of consumers through the oral-gut-vaginal route. We have identified the strain <i>L. gasseri</i> CECT 30648, which shows great probiotic properties, including antagonism against several relevant urogenital pathogens, can colonize the vaginal tract of >55% of participants, and can modulate vaginal microbiota toward a lactobacillus-dominated status in a randomized controlled clinical trial in healthy premenopausal women. These results suggest that oral consumption of <i>L. gasseri</i> CECT 30648 might be effective in promoting vaginal health.