Targeted High-Resolution Taxonomic Identification of Bifidobacterium longum subsp. infantis Using Human Milk Oligosaccharide Metabolizing Genes

Bifidobacterium longum subsp. infantis ( B. infantis ) is one of a few microorganisms capable of metabolizing human breast milk and is a pioneer colonizer in the guts of breastfed infants. One current challenge is differentiating B. infantis from its close relatives, B. longum and B. suis . All three organisms are classified in the same species group but only B. infantis can metabolize human milk oligosaccharides (HMOs). We compared HMO-metabolizing genes across different Bifidobacterium genomes and developed B. infantis -specific primers to determine if the genes alone or the primers can be used to quickly characterize B. infantis . We showed that B. infantis is uniquely identified by the presence of five HMO-metabolizing gene clusters, tested for its prevalence in infant gut metagenomes, and validated the results using the B. infantis -specific primers. We observed that only 15 of 203 (7.4%) children under 2 years old from a cohort of US children harbored B. infantis . These results highlight the importance of developing and improving approaches to identify B. infantis . A more accurate characterization may provide insights into regional differences of B. infantis prevalence in infant gut microbiota.