Baby 2 Baby Beneficial Bacteria

The investigators will recruit mother-infant dyads to attend weekly lactation support groups for five weeks and randomize infants to receive either an HMO consuming (B. longum subsp. infantis) or non-HMO consuming (L. reuteri) probiotic. The investigators will collect a baseline infant stool sample and maternal milk sample before attendance at the first lactation support group meeting. At the first support group meeting, mothers will be provided with the open label probiotic their infant was randomized to receive, and will give the probiotic daily for the next 28 days. The investigators will collect a second infant stool sample and a second milk sample at the final lactation support group meeting. The investigators will use qPCR and metagenomic sequencing to test if the study probiotics or other bacteria transmit from the infants who received a specific species to the infants who did not receive that species. We will also test to see if the probiotic given to infants is detectable in milk samples. The investigators anticipate HMO consuming bacteria will and non-HMO consuming bacteria will not transmit between infants.