Practical media formulations for rapid growth of Lactobacillus iners and other vaginal bacteria

The composition of the vaginal microbiome is closely tied to host health. Bacterial vaginosis (BV), caused by the overgrowth of specific anaerobes (e.g., Gardnerella vaginalis), is associated with negative health outcomes. A vaginal microbiome dominated by Lactobacillus species is thought to protect against BV. However, the role of Lactobacillus iners is controversial, with evidence suggesting that some strains may not protect against BV while others do. To better characterize L. iners strains, their interactions with vaginal bacteria and human cells need to be investigated in vitro, but this has been impeded by the lack of liquid media that supports rapid L. iners growth. We have developed three liquid media formulations for L. iners growth: Serrador's Lactobacillus-adapted Iscove's medium (SLIM), which supports robust L. iners growth; a vaginally adapted version of SLIM (SLIM-V); and a chemically defined version (SLIM-CD). SLIM and SLIM-V improve L. iners growth compared to previously published formulations and also support the growth of other vaginal bacteria, including Lactobacillus crispatus, Lactobacillus jensenii, Lactobacillus gasseri, and Gardnerella vaginalis. SLIM-CD leads to slower growth but may be useful for characterizing L. iners nutrient requirements or metabolite production. Importantly, SLIM and SLIM-V also support the growth of human vaginal epithelial cells, providing a foundation for future co-culture studies. Here, we present the formulations of SLIM, SLIM-V, and SLIM-CD and compare the growth of bacterial strains and human cells in these media.IMPORTANCELactobacillus iners is one of the most prevalent members of the vaginal microbiome, but whether it promotes health or leads to bacterial vaginosis is not well understood. We have developed media formulations that lead to improved L. iners growth and support growth of other vaginal bacteria and human vaginal cells. This will allow for investigation of how L. iners interacts with vaginal bacteria and the host, improving our understanding of its role in the vaginal microbiome.