B. thetaiotaomicron monoculture and B. thetaiotaomicron + A. caccae co-culture showed differential utilization of human milk oligosaccharide (HMOS) structures. The percentage of HMOSs left in B. thetaiotaomicron monoculture is significantly higher (p < 0.05) than B. thetaiotaomicron + A. caccae co-culture at 24 and 48 h for all structures. Error bars represent the error propagation for the mean of three (for A. caccae) or four (for B. thetaiotaomicron and B. thetaiotaomicron + A. caccae) biological replicates measured in technical triplicates. The blank control was measured only in technical triplicates. Abbreviations: 2′-FL, 2′-fucosyllactose; 3-FL, 3-fucosyllactose; DFL, difucosyllactose; LNT, lacto-N-tetraose; LNnT, lacto-N-neotetraose; LNFP I, lacto-N-fucopentaose I; LNFP II, lacto-N-fucopentaose II; LNFP III, lacto-N-fucopentaose III; LNFP V, lacto-N-fucopentaose V; SL, sialyllactose.