15N-labeled N-acetylglucosamine (NAG) fed to B. infantis cells are incorporated into its proteome. This indicates that NAG, an amino sugar residue of human milk oligosaccharides (HMO) and other biopolymers, is used as a nitrogen source. Transcriptomics while subsisting on NAG nitrogen are consistent with the proteomics results. This further indicates that B. infantis utilizes NAG nitrogen in and shunts it towards a fundamental cellular processes.