Yeasts, molds found in daycare centers may impact future allergy, asthma development

March 03, 2022

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The indoor mycobiomes at Norwegian daycare centers included considerably more yeasts and molds than the outdoor areas around them, according to a study published in Applied and Environmental Microbiology.

Such environments could impact the future development of allergies and asthma in children.

Source: Adobe Stock

“Children spend considerable time in daycare centers, where they are exposed to the indoor mycobiome. However, the indoor mycobiome is not well explored,” author Eva Lena F. Estensmo, PhD, of the section for genetics and evolutionary biology in the department of biosciences at University of Oslo, Norway, told Healio.

Lena F. Estensmo

“With the increase in chronic diseases like asthma and allergies in children, we wanted to investigate the indoor mycobiome in daycare centers, as it might be important for the children’s health,” Estensmo continued.

Fungal growth can lead to poor indoor air quality, the researchers said, and some fungi are associated with allergic reactions and respiratory symptoms that may lead to chronic respiratory diseases.

The researchers selected 125 daycare centers distributed along different environmental gradients throughout Norway. Using a community science approach, the researchers instructed the staffs at these daycare centers to collect and return samples for analysis.

Staff members collected 572 dust samples from doorframes in each daycare center’s bathroom and main room, representing the indoors, and doorframes around each daycare center’s main entrance, representing the outdoors.

The final dataset included 748,836 sequences, with 1,342 sequences in each of the 558 samples used in DNA metabarcoding analysis as well as 5,956 fungal operational taxonomic units detected in total.

“Using DNA sequencing, we revealed a high diversity of fungi in daycare centers throughout Norway,” Estensmo said.

The fungal community compositions of the main room and bathroom samples largely overlapped, the researchers said, but they were clearly different from the compositions of the samples taken from the main entrances.

Saccharomycetales and Mucorales were the most common genera in the indoor mycobiomes, while Pucciniales, Capnodiales, Agaricales and Chaetothyriales dominated the outdoor mycobiomes.

Yeasts, dimorphic yeasts and molds were considerably more abundant in the indoor mycobiomes, and saprotrophs, plant pathogens and lichens were more common in the outdoor mycobiomes.

“Many of the indoor fungi are of outdoor origin, and therefore the outdoor conditions, like climate and vegetation, influence which fungi are present indoors. However, many molds, and especially yeasts, were far more common indoors than outdoors, and many of these probably have mainly indoor sources,” Estensmo said.

“In support of this, we observed that certain building features but also the number of ‘inhabitants’ play in on which fungi are present. The high diversity of yeasts especially came as a surprise, of which many might be associated with the human body,” she continued.

Debaryomyces and Candida, which were two of the top 50 true yeasts found in the indoor samples, are associated with the human body. Candida is particularly associated with children and can cause oral thrush in some cases, the researchers said. Along with Malassezia, Candida also is associated with inflammatory skin disorders such as seborrheic dermatitis and atopic dermatitis in childhood and adulthood.

Extremotolerant molds such as Mucor, Penicillium, Aspergillus and Wallemia also were abundant in the indoor samples. The researchers did not establish a causal relationship, but they did note that some of these mold taxa also were abundant in the homes of children with allergies and respiratory diseases.

Variables such as the type of daycare center, the year the center was constructed, the number of departments in the center, pests and type of building impacted variations in the indoor mycobiome. Temperature, total insolation and other climactic variables also correlated with indoor mycobiome composition.

Specifically, longitude as an indicator of regional climate, pests and rodents, construction year and number of children attending the center were the main drivers behind the fungal community composition, although these factors only accounted for 7% of the variations in mycobiome compositions.

Young children often bring organic materials such as soil and litter from nature into daycare centers, so these facilities may accumulate extra organic substrates promoting fungal growth, compared with other indoor environments, the researchers said. In fact, previous research has shown that daycare centers have higher concentrations of fungi than homes do, the researchers continued.

“It is important to be aware that the indoor mycobiome can be important for the children’s health. We know that fungi in the indoor environment may cause chronic diseases like asthma and allergies,” Estensmo said.

Previous research has focused on a few fungi that are known to be harmful, though very little is known about the overall fungal community that is indoors and present in the everyday lives of human beings, she said.

“The high-throughput sequencing technique provides the opportunity to explore the overall fungal community, not only the few well known,” Estensmo said. “It is only when we know who they are and what they are doing that we can decide if they are harmful or beneficial for our health.

Estensmo further said that “we are still scratching the surface,” and more studies are needed. She and her colleagues are continuing their work by comparing the indoor mycobiomes of daycare centers to those found in private homes.

“The high diversity of yeasts in the indoor environments of daycare centers came as a surprise to us. They should be investigated further to better understand their effects on human health,” she said. “In the future, one should also obtain more precise quantitative data on the fungal abundances.”

Reference:

For more information:

Eva Lena F. Estensmo, PhD, can be reached at [email protected].