Human Milk Oligosaccharides Modulate Nitrogen Utilization in Lactobacillus crispatus in a Glucose-Dependent Manner

The vaginal microbiome's transition to a dysbiotic state increases susceptibility to pathogens like group B Streptococcus. While human milk oligosaccharides are established prebiotics in the neonatal gut, their impact on the vaginal niche remains largely unexplored. This study investigated the effects of pooled human milk oligosaccharides on the growth and physiology of vaginal (Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus iners) and gut-derived (Lactobacillus reuteri, Lactobacillus rhamnosus) commensals. Growth analyses revealed that human milk oligosaccharides significantly and selectively stimulated growth across all vaginal strains tested, whereas gut commensals exhibited variable or inhibited growth. Carbohydrate utilization assays and comparative genomics against Bifidobacterium infantis showed that Lactobacillus crispatus and Lactobacillus reuteri lack the canonical metabolic machinery to catabolize human milk oligosaccharides. Instead, nitrogen utilization assays identified a glucose-dependent pathway where human milk oligosaccharides are associated with the depletion of primary amines and amino acids in Lactobacillus crispatus supernatants. These results suggest that human milk oligosaccharides act as noncatabolic modulators of vaginal lactobacilli. Collectively, these in vitro findings may warrant investigation of human milk oligosaccharides as modulators of vaginal commensal physiology in more complex experimental systems.