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Page 14 of 19 Klaassens et al. Microbiome Res Rep 2024;3:38 https://dx.doi.org/10.20517/mrr.2024.13

Figure 6. PCA analysis at the strain level from samples after 48 hours in the ex vivo model of the infant bacterial ecosystem. PCA:
Principle Coordinate Analysis; VD: fecal inoculum derived from vaginally delivered infant; CS: fecal inoculum derived from cesarean-
delivered infant; Blank: no probiotics; iPF: intact protein formula; GOS: galactooligosaccharides; eHF: extensively hydrolyzed formula;
Bb: B. breve DSMZ 32583; Lf: L. fermentum CECT 5716; Lf + Bb: both probiotics added.

Breastfeeding is the best possible nutrition for infants. Isolating probiotic strains from HM is a potential
method to transfer this HM-mediated protection to children who cannot be breastfed. Bb was isolated from
HM and recently assessed for probiotic health effects and safety . Lf, which was isolated from HM many
[41]
[42]
years ago, has demonstrated health-promoting mechanisms in preclinical and human studies . Recently, it
was shown in a large infant cohort that the combination of Lf and GOS could modify the overall infant
microbiota composition closer to the breastfed reference group at the age of four months . While only
[43]
being present in low abundance as shown here, the administration of Lf was shown to exert positive effects
[43]
on respiratory pathologies despite low abundance in the stool microbiota in this cohort. Positive effects
[44]
on health outcomes despite the low abundance of the probiotics in the microbiota have been observed for
this strain by others before .
[45]
The addition of probiotics to food and the associated microbial activity and generation of SCFA can be
associated with gas formation, especially in combination with prebiotic compounds [46,47] . Interestingly, here,
the combination of two probiotic strains abolished the gas formation found for a single probiotic in vitro,
suggesting cross-feeding mechanisms. These cross-feeding mechanisms might also be seen through the
enantioselective degradation of L-Lactate throughout the observation period [48,49] . While these effects were
significant in vitro, no effects were visible anymore in the presence of a complex host microbiota, indicating
the involvement of other members of the donor microbiota in these cross-feeding mechanisms.