The invention pertains to the benefits of Propionibacterium freudenreichii supplementation in infant foods, for example, preterm infant foods such as human donor milk or infant milk formula. Accordingly, the invention provides a method of administering an infant food comprising a pharmaceutically effective amount of P. freudenreichii to an infant, for example, a preterm infant. The invention also provides infant food compositions comprising a pharmaceutically effective amount of P. freudenreichii. Further, the invention pertains to methods of determining a pharmaceutically effective amount of P. freudenreichii which provides beneficial effects to a subject, for example, induction of regulatory immunity and/or induction of protective immunity. Also provided are compositions capable of modulating the immune response of humans and non-human mammals and methods of modulating the immune response of a subject using said compositions.
