Exploring the molecular crosstalk between the sex steroids drospirenone and ethinylestradiol with vaginal lactobacilli

Introduction The vaginal microbiota, dominated by the genus Lactobacillus spp., plays a crucial role in maintaining vaginal homeostasis and protecting against infection through lactic acid production, antimicrobial compound secretion and competitive exclusion of pathogens. Although hormonal fluctuations are known to influence microbial composition, the molecular mechanisms underlying these interactions remain largely unexplored. The aim of this study was to investigate the direct effects of the synthetic sex hormones drospirenone and ethinylestradiol, key components of hormonal contraceptives, on representative vaginal Lactobacillus species. Methods Representative Lactobacillus species associated with different vaginal Community State Types (CSTs) were exposed to drospirenone and ethinylestradiol under simulated vaginal conditions. Lactobacilli responses were assessed using growth assays and RNA-seq transcriptome profiling to evaluate species-specific transcriptional changes following hormonal exposure. Results Among the tested strains, Lactobacillus crispatus PRL2021 showed the most pronounced transcriptomic modulation. In this strain, hormone treatment led to the upregulation of genes involved in cell wall biosynthesis, amino acid and carbohydrate metabolism, and stress adaptation. Specifically, expression of the histidine kinase gene sasA_1 , part of a two-component regulatory system potentially involved in environmental sensing, was induced. Additionally, the ribBA and ribE genes, predicted to be involved in riboflavin biosynthesis and associated with antioxidant defense and mucosal protection, were upregulated. Conclusion These findings demonstrate that drospirenone and ethinylestradiol can directly modulate bacterial gene expression, revealing a previously underinvestigated molecular crosstalk between host endocrine signals and the vaginal microbiota. This interaction may contribute to the maintenance of vaginal eubiosis and has potential implications for the development of microbiome-targeted strategies to support women’s health. Further studies are needed to elucidate the broader functional consequences of hormone–microbiota interactions and their clinical relevance.