Korea University study proposes first toxicity-based exposure limits proposed for indoor airborne fungi
Scientists from Korea use animal toxicity data to set microbial safety thresholds for indoor air, challenging current standards
Korea University College of Medicine
Microbial contaminants like airborne bacteria and fungi can make up more than a third of indoor air pollution. Yet, while many countries regulate chemical pollutants, most have no legally binding thresholds for microbial exposure, particularly fungi. This lack of toxicological benchmarks leaves a major gap in indoor air safety policy.
Addressing this gap, a new study led by Professor Wonsuck Yoon of Korea University provides the first species-specific health risk estimates for indoor airborne microbes based on animal toxicity data. This study was made available online on June 9, 2025, and was published on Sep 5, 2025, in Volume 495 of the Journal of Hazardous Materials. This is the first study to estimate human health risks from indoor microbes using benchmark doses derived from animal toxicity data.
Prof. Yoon and his team collected microbial samples from more than 500 high-traffic indoor environments across South Korea, including restaurants, retail stores, and public transit hubs, and identified the most prevalent fungi and bacteria. Four representative species were then selected for controlled exposure studies in mice. Over four weeks, the animals were repeatedly administered doses of these inactivated microbes via their airways.
The results showed clear toxic effects: elevated levels of inflammatory cytokines, increased immune cell infiltration, and lung tissue damage, more specifically from fungal species. Based on these findings, the team calculated species-specific benchmark dose values and converted them into estimated safe exposure limits for humans.
“This work is a part of a national initiative on the health impact of indoor biological agents and highlights the limitation of total microbial load regulation, emphasizing that health risks can vary significantly by species,” said Prof. Yoon.
The study determined that exposure to fungi may be unsafe even at levels below current South Korean and World Health Organization guidelines. By contrast, the estimated safe limits for bacteria were consistent with existing regulations. These findings could inform multiple applications: regulatory policy, building health certification, performance standards for air purifiers, and occupational safety in high-density spaces.
The researchers emphasize the longer-term importance of moving beyond crude microbial counts. “This approach will enable safer, smarter, and better health-optimized indoor environments across diverse urban and residential settings,” said Prof. Yoon.
While the study offers a valuable first step toward species-specific microbial standards, the authors note that it was based on inactivated microbes and limited to culturable strains. Future work should include viable organisms and more comprehensive indoor microbiome assessments to better reflect real-world exposure and risks.
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Reference
Title of original paper: Assessment of pulmonary toxicity in mice to evaluate human health risks from indoor airborne microorganisms
Journal: Journal of Hazardous Materials
DOI: 10.1016/j.jhazmat.2025.138884
About Korea University College of Medicine
Korea University College of Medicine is the medical school of Korea University. It is located in Seoul, South Korea. As one of the oldest medical schools in South Korea, it has been historically regarded as one of the country's top medical schools. The school was founded as Chosun Women's Medical Training Institute in 1928 by Rosetta Sherwood Hall. The institute was subsequently renamed several times and ultimately merged with Korea University to become Korea University College of Medicine. So far, the school has produced over 7,000 graduates, most of whom are working as prominent physicians and public health advocates worldwide.
Website: https://medicine.korea.ac.kr/en/index.do
About the author
Prof. Wonsuck Yoon is the lead author and director of the Air Microbiome Health Research Institute and a professor at Korea University College of Medicine, affiliated with the Allergy and Immunology Research Center. He serves as the principal investigator of the Korean Ministry of Environment’s Indoor Air Biological Hazards Health Impact Assessment Program. His research integrates microbiome science with environmental toxicology, focusing on the health effects of airborne microbes. He also serves as the only board member from Asia in the EAACI (European Academy of Allergy and Clinical Immunology) Working Group on One Health.
Journal
Journal of Hazardous Materials
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Assessment of pulmonary toxicity in mice to evaluate human health risks from indoor airborne microorganisms
Article Publication Date
5-Sep-2025
Uncovering the hidden emerging pathogen behind Aspergillosis cases in Japan
Scientists discover ancestral evolutionary links of Aspergillus latus strains through in-depth genome sequencing analyses
Chiba University
image:
Through extensive phylogenetic analyses based on utilizing cloned copies of the calmodulin gene, researchers have mapped the evolutionary genetic relationships between Aspergillus spinulosporus and A. sublatus strains, giving rise to the allodiploid hybrid A. latus strain.
view moreCredit: Professor Hiroki Takahashi from Chiba University, Japan
Aspergillus is a fungus that is commonly found in the environment, both indoors and outdoors. This fungus species can cause aspergillosis—a respiratory infection affecting the lungs. A. fumigatus, A. nidulans, and A. niger are some of the common species within the Aspergillus genus that cause aspergillosis. In high-risk populations, such as immunocompromised individuals, aspergillosis can be life-threatening and lead to poor patient outcomes.
Previous research studies have identified A. latus as an allodiploid hybrid species containing gene sequences from two distinct species: A. spinulosporus and an unknown species related to A. quadrilineatus. Owing to its allodiploid hybrid nature, A. latus has been associated with both colonization and clinical disease, including invasive pulmonary aspergillosis, and some strains have shown reduced susceptibility to antifungal agents. Recent reports indicate that certain European and American aspergillosis cases could be attributed to A. latus. However, to date, A. latus strains have not been identified in clinical samples of patients in Japan.
To identify and characterize A. latus strains from clinical isolates and address the concerns around cryptic species of Aspergillus that lack definite and observable morphological characteristics, a team of researchers led by Associate Professor Hiroki Takahashi from the Medical Mycology Research Center, Chiba University, Japan, has conducted a new study. The research team comprised Dr. Saho Shibata, Dr. Momotaka Uchida, and Dr. Takashi Yaguchi from the Medical Mycology Research Center, Chiba University, along with Dr. Vit Hubka from the Czech Academy of Sciences, Czech Republic. Their findings were published in Volume 63, Issue 6 of Medical Mycology on June 10, 2025.
“The complexity of fungal pathogens and their resistance mechanisms presents both a fascinating scientific challenge and an important public health issue, which I am eager to explore,” says Dr. Takahashi, explaining the motivation behind the present study. Initially, the researchers analyzed 23 A. spinulosporus strains, which were collected between 2012 and 2023.
To accurately identify A. latus strains among the samples, the team utilized comprehensive phenotyping and genome sequencing analysis. The team identified seven A. latus strains among the 23 samples, which are clinically significant given that A. latus strains were not previously reported in Japan. Furthermore, through phylogenetic analyses, they observed that while one copy of the calmodulin gene aligned with the genetic sequence of A. spinulosporus, the other copy clustered with A. sublatus.
Inspired by their findings, the researchers went a step further and conducted antifungal susceptibility testing of different Aspergillus strains to antifungal medications. Japanese strains of A. latus showed reduced susceptibility to caspofungin and amphotericin B drugs. Also, genomic analysis revealed multiple amino acid insertions and deletions in one of the two alleles of the fks1 gene, which encodes a key component of the fungal cell wall biosynthesis machinery. This fks1 gene is associated with resistance to echinocandin-class antifungal drugs. The researchers suggest that if overlapping nucleotide signals are observed during gene sequencing—such as double peaks indicating the presence of two distinct alleles—then the possibility of hybrid species like A. latus should be considered in the diagnostic evaluation.
Highlighting the potential applications of the present study, Dr. Takahashi states, “By incorporating molecular phylogenetic and genomic analyses into diagnostic systems, our research is expected to improve the accuracy of fungal infection diagnoses and enable the selection of the most appropriate antifungal treatments for individual patients.”
Taken together, this study provides significant observations regarding the clinical relevance, prevalence, and potential role of A. latus as a disease-causing agent. Improved and reliable molecular diagnostic tools are vital for the accurate identification of A. latus strains and the subsequent management of aspergillosis.
About Associate Professor Hiroki Takahashi from Chiba University
Dr. Hiroki Takahashi serves as an Associate Professor at the Medical Mycology Research Center, Chiba University, Japan. He has been actively involved in projects for the systems biology of microorganisms in the division of bio-resources. His main topics of research include the transcriptome of fungi, mathematical models in microorganisms, and next-generation sequencing data analysis. Over the years, Dr. Takahashi has published 94 papers that have been cited more than 7,000 times.
Journal
Medical Mycology
Method of Research
Experimental study
Subject of Research
Cells
Article Title
Aspergillus latus: A cryptic causative agent of aspergillosis emerging in Japan
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