Figure 2.

Established and putative bacterial transmission routes between uterine microbiome and distal sites. (A) Putative hematogenous spread of bacteria emanating from the gut and oral microbiome or other means of circulation of bacteria through the blood. Viability has been demonstrated to be conserved during translocation through blood with intracellular dormancy being an example of how bacteria remain viable in blood. (B) Ascension of bacteria through the cervix has been well established and is a likely source of bacterial transmission. (C) Transmission of bacteria through routes, other than those illustrated, include assisted reproductive technology-related gynecologic procedures whereby bacteria from the vaginal microbiome are introduced to the uterus, such as oocyte retrieval. Other routes of colonization may exist beyond hematogenous spread. The insertion or removal of intrauterine devices may introduce bacteria into the uterus as well as potentially aid in ascension through the “tails” that extend from the uterus through the endocervical canal.