Bifidobacteria constitute one of the dominant groups of microorganisms colonizing the human gut of infants.
Their ability to utilize various host-derived glycans as well as dietary carbohydrates has received considerable
scientific attention. However, very little is known about the role of fermented foods, such as kefir, or their constituent
glycans, such as kefiran, as substrates for bifidobacterial growth and for the modulation of the expression of
bifidobacterial host-effector molecules. Here, we show that Bifidobacterium bifidum PRL2010 exhibits high
growth performance among the bifidobacterial strains tested when cultivated on kefir and/or kefiran polymer.
Furthermore, a 16S rRNA metagenomic approach revealed that the microbiota of kefir is modified upon the
addition of PRL2010 cells to the kefir matrix. Finally, our results show that kefir and kefiran are able to influence
the transcriptome of B. bifidum PRL2010 causing increased transcription of genes involved in the metabolism of
dietary glycans as well as genes that act as host–microbe effector molecules such as pili. Altogether, these data
support the use of kefir as a valuable means for the delivery of effective microbial cells in probiotic therapy.