The vaginal microbiome of transgender men receiving gender affirming hormonal therapy in comparison to cisgender woman
Background: The vaginal microbiome of trans men (TM) and menopausal women is suspected to be similar due to the lack of estrogen and Lactobacilli. Vaginal microbiomes deficient in Lactobacilli are associated with impaired epithelial maturation, increased mucosal inflammation, changes in epithelial barrier integrity, and increased susceptibility to sexually transmitted infections.  Results: The vaginal microbiome of TM showed a higher Alpha diversity than the two control groups, but was more similar to the microbiome of postmenopausal women. Alpha diversity decreased significantly with length of amenorrhea in TM and postmenopausal women when looking at the Shannon index. Various beta-diversity measures (Bray-Curtis, Weigthed Unifrac, Unweighted Unifrac), showed a significant difference in the community composition between the TM-group and the premenopausal group (p < 0.001) as well as between the TM-group and the postmenopausal group (p < 0.001). The vaginal microbiome of TM is characterized by a loss of Lactobacillus and an increase in bacteria more commonly associated with the intestinal flora (e.g. Campylobacter, Anaerococcus, Dialister, Prevotella) compared to the premenopausal group. Sexual activity is associated with lower levels of Prevotella and Streptococcus. The abundance of Dialister and Prevotella decrease with length of GAHT in TM.  Conclusions:   The vaginal microbiome of TM differs significantly from the vaginal microbiome of premenopausal women but shows similarities to postmenopausal women. The length of amenorrhea, GAHT and sexual activity have an important impact on vaginal microbiome and thus possibly on risk of infections. A deeper understanding of the composition of the vaginal microbiome is crucial for improving vaginal health.