Described in several exemplary embodiments are Bifidobacterium longum subspecies, microorganisms and formulations thereof. Described in several exemplary embodiments are formulations, such as synthetic formulations, that contain one or more of the Bifidobacterium longum subspecies microorganisms. Described in several embodiments herein is use of the Bifidobacterium longum subspecies microorganisms and formulations thereof, such as in an infant and/or young child.