Forgotten fungi: yeasts and other fungi inhabit breast milk alongside bacteria and are shaped by both geographic location and mode of delivery

Previous research has widely studied the impact of early-life factors—related to both infant and mother—on milk microbiota diversity and composition. However, until now, scientists have focused mainly on the milk’s bacterial fraction without exploring the contribution of other commensal microorganisms such as colonizing fungi (the mycobiome).

A new study, led by Dr. Maria Carmen Collado from the Institute of Agrochemistry and Food Technology, which is part of the Spanish National Research Council, in Valencia (Spain), has revealed that the breast milk microbiome is an important source of fungi for the growing infant.

GMFH editors corresponded with the authors via email to clarify the relevance of their work.

This research has its roots in a previous study in which the authors demonstrated, using different techniques, the presence of viable fungi in breast milk from 65 healthy lactating Spanish women.

In the new study, the authors analyzed breast milk samples from healthy adult women in South Africa, Finland, China and Spain with normal weight (20 women/country) in order to investigate the potential influence of geographic location and the mode of delivery on mycobiota presence and composition. The presence of fungi in milk samples was analyzed by both a quantitative polymerase chain reaction of fungal ribosomal ribonucleic acid and by culture and isolates characterization.

Malassezia and Davidiella were the most abundant genera across the four countries, regardless of geographical area and mode of delivery. Furthermore, milk samples from all participants shared a core mycobiota consisting of Malassezia, Davidiella, Sistotrema, and Penicillium.

Despite these shared patterns across all women, however, geographic location and delivery mode led to specific shifts in mycobiome composition. “Our data support the potential role of breast milk in the initial seeding of fungal species when colonizing the infant gut,” says Maria Carmen Collado.

“The current report describes a core of four genera shared across continents, consisting of Malassezia, Davidiella, Sistotrema, and Penicillium, all of which have also been reported to be present in the infant gut. Little is known about the mycobiota but recent studies are showing their relevance for infant health,” says co-author Alex Mira.

The detectable levels of fungal deoxyribonucleic acid varied across countries, highlighting the breast milk mycobiome’s dynamics depending on geographic location. Spanish and South African samples achieved the highest levels of fungi (80% and 70%, respectively), followed by Chinese samples (45%) and, finally, those from Finland (35%).

Although mode of delivery did not affect either fungal diversity or richness, specific fungi genera such as Cryptococcus were more abundant in samples from mothers who delivered their babies vaginally. The functional implications of these results for the health of a growing infant deserve long-term follow up studies that take into account breast milk’s mycobiome in addition to its bacterial populations.

When exploring milk mycobiota interactions with bacteria, the authors found multiple interactions, both intra- and inter-samples, depending on the country of origin, delivery mode and maternal factors such as age and body mass index.

In conclusion, this study has characterized the breast milk mycobiome of healthy adult women, with geographical location and mode of delivery major as modulators of its composition. Now that a fungal community has been characterized in breast milk, future work should explore its origin and impact on infant health.

“Our findings open new research possibilities and support the need for studying breast milk as a personalized food beyond nutritional aspects,” the authors write. Only a few yeasts are currently used as probiotics and the authors highlight the possibility of identifying more fungal species that could potentially confer benefits for infant health.

References:

Boix-Amorós A, Martinez-Costa C, Querol A, et al. Multiple approaches detect the presence of fungi in human breastmilk samples from healthy mothers. Sci Rep. 2017; 7(1):13016. doi: 10.1038/s41598-017-13270-x.

Boix-Amorós A, Puente-Sánchez F, du Toit E, et al. Mycobiome profiles in breast milk from healthy women depend on mode of delivery, geographic location and interaction with bacteria. Appl Environ Microbiol. 2019; doi: 10.1128/AEM.02994-18.