Writing in Applied and Environmental Microbiology, the international research team demonstrate the presence of fungi and yeasts in the breast milk microbiome of mothers in multiple countries.
They noted that multiple previous studies have identified specific bacteria that are present in breast milk, and that certain fungi and bacteria have been shown to be important for infant health.
"Our research demonstrates the presence of yeasts and other fungi in breast milk in healthy mothers, supporting the hypothesis that breast milk is an important source of microorganisms to the growing infant," said lead researcher Maria Carmen Collado, from the Institute of Agrochemistry and Food Technology at the Spanish National Research Council.
Having previously identified the presence of yeasts and other fungi in breast milk from mothers in Spain, the research team then looked to sample mothers' breast milk in other geographic locations, including Finland, China, and South Africa – to find out whether the original findings held up in locations with different weather, diets, and lifestyles from those in southern Europe.
"Our data confirm the presence of fungi in breast milk across continents and support the potential role of breast milk on the initial seeding of fungal species to the infant gut," said the authors. "This supports the existence of a 'breast milk mycobiota' under healthy conditions."
Collado and her colleagues analysed a total of 80 mature breast milk samples from four different countries using Illumina sequencing of the ITS1 region, joining the 18S and 5.8S regions of the fungal rRNA region.
They reported that the genera Malassezia and Davidiella were most prevalent across the different countries.
The investigators also compared the breast milk mycobiome in mothers who had delivered vaginally with that from mothers who had delivered via cesarean section.
Specific fungi, such as those of the genus Cryptococcus, were more prevalent among samples from mothers delivering vaginally, but mode of delivery made no difference in fungal diversity or richness, they said.
“A core formed by Malassezia, Davidiella, Sistotrema and Penicillium was shared in the milk samples from the different origins, although specific shifts in mycobiome composition were associated with geographic location and delivery mode,” wrote the authors
More than 70% of Spanish and South African samples had detectable levels of fungal DNA, while only 45% of Chinese samples and only 35% of Finnish samples did so.
Despite the similarities of the mycobiomes across the four countries, Collado noted the findings also reinforce the potential influence of environmental factors, in particular geographic location, on the species of yeast and fungi that make up the breast milk mycobiome.
The identification of viable fungal cells within breast milk suggest that breast milk could influence development of infants' mycobiota, said the research team.
"However, little is known about the development of mycobiota in infants," said Collado.
"Currently, some yeast species are used as potential probiotics to promote infant health," she noted. "The most common one is Saccharomyces boulardii.”
“Our study identifies more fungal species that could potentially confer benefits for human health, and the possibility of isolating appropriate strains from breast milk. Those potential benefits should now be studied in detail."
Source: Applied and Environmental Microbiology
Published online ahead of print, doi: 10.1128/AEM.02994-18
“Mycobiome profiles in breast milk from healthy women depend on mode of delivery, geographic location and interaction with bacteria”
Authors: Alba Boix-Amorós, et al