Fungi Fact Sheet
What are Fungi?
Fungi are eukaryotic, heterotrophic organisms. Fungi include both single-celled yeasts and multi-cellular filamentous fungi. Many fungal species are able to survive in oligotrophic environments (which are areas relatively low in plant nutrients and containing abundant oxygen in the deeper parts). Fungi scavenge nutrients from the substrate that they colonize, or from the air or water in which they live. Fungi can produce secondary metabolites, some of which are toxins. Some fungal species and the metabolites they produce are human pathogens or allergens.
Fungi spend most of their lives buried in their food source, which can be a live host such as a plant, animal, or it can be dead material/soil. Some fungi can make fruit bodies, like mushrooms, annually; others might only do so every few years.
Fungi do not ingest food in the same manner in which animals do, but they do release enzymes into their surrounding environment to break down complex materials into simpler materials that can be absorbed by the fungus in a process known as absorptive nutrition. Water is necessary for these enzymes to leave the fungus, remain functional, and to break down complex substances. Once the complex substances have been broken down and dissolved in water, they are then absorbed by the fungus.
How can they enter water sources?
For fungal growth to occur, a certain level of free water needs to be present. Different fungi have different water requirements. Physical openings in storage facilities and lack of cover allow microorganisms to be introduced from the air, animals, introduction of untreated surface or groundwater.
The problems associated with fungi include blockage of water pipes, organoleptic deterioration, pathogenic fungi and mycotoxins. Mycotoxins are secondary metabolites only produced and released under certain conditions that can cause various health effects in humans and animals. The secondary metabolites produced by some species can alter the taste and smell of water. Organic acids produced by fungal metabolic processes can increase the rate of corrosion in water pipes.
The water that is available that can support microbial life in building materials is commonly expressed as water activity. Water activity compares the physical properties of water in the material in question with that of pure water to generate a scale from 0-1.0. Pure distilled water has a value of 1.0. Although there is no sampling device that directly tests for water activity; instead the equilibrium relative humidity is reported.
High-risk areas for soil-borne fungal growth to occur are treatment breakthrough, intrusion, cross connections, and main repairs/ breaks. Main breaks include leaking joints, adapters, cracks in pipelines, and deficient seals. Low and negative pressure events can allow intrusions of contaminants through such breaks. Changes in pressure can arise from pump startup and shutdown, flushing operations, power failure, and large changes in demand. Airborne species may be introduced from the air in contact with stored water.
Once the species is introduced into the environment, it can become established on the inner surfaces of pipes, including the interaction and reaction with sealings, coatings, and biofilms within distribution systems, or suspended in the water. Some species can be found throughout water distribution networks, while other can be restricted to localized sites.
Presently, regulations controlling levels of fungi in drinking water are rare. For example, in the UK the fungi are not required to be monitored or controlled.
Without water, fungi are unable to grow or reproduce. A key to preventing and controlling fungal growth in things such as buildings can be to reduce the availability of free water by removing the water source such as repairing leaks in pipes, running a dehumidifier in damp areas, and removing wet building materials.
How can fungi affect humans?
Many fungal species can be resistant to water treatment and disinfection. The water treatment process may fail to remove/ inactivate all microorganisms of concern from source water.
The four principal pathways by which people can be exposed to fungi in drinking water are:
Ingestion by drinking contaminated water
Inhalation of aerosolized spores while showering or in the sauna
Skin contact with contaminated water, like showering or bathing
Introduction through mucous membranes such as the skin, eyes, and oral cavity while showering or bathing
Anaissie et al. attempted to identify sources of Aspergillus infection in a hospital. They found that bathrooms had significantly higher numbers of airborne propagules than in patients’ rooms. This increase was thought to be caused by aerosalisation following running the tap, the shower, or flushing the toilet, which allowed for colonization of damp micro-niches within the bathroom. It was also found that airborne A. Fumigatus levels increased after running the shower multiple times.
Some species have the potential to cause allergic reactions and disease. There is a risk of superficial or localized infection in healthy individuals and more severe and invasive infection in immune-compromised patients. Water contaminated with fungi is of importance to hospitals where immunocompromised patients undergo treatment. Fungi present in drinking water may cause severe fungal infections in immunosuppressed patients. In a small number of studies, drinking water supplies have been found to be the source of infection. Aspergillus accounts for most infections, with Aspergillus fumigatus accounting for 90% of cases.
Although there are some indications of fungal species affecting humans, little research has been conducted on the matter and more needs to be conducted to ensure that no harmful long-term effects are possible.
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Resources:
Anaissie, E.J., Stratton, S.L., Dignani, M.C., Summerbell, R.C., Rex, J.H., Monson, T.P., Spencer, T., Kasai, M., Francesconi, A. and Walsh, T.J., 2002. Pathogenic Aspergillus species recovered from a hospital water system: a 3-year prospective study. Clinical Infectious Diseases, 34: 780-789.
Bradbury Science Museum. 2018. How many species of fungi are there? https://www.lanl.gov/museum/news/newsletter/2018/01/fungi.php
Department for Environment Food and Rural Affairs. April 2011. A review of fungi in drinking water and the implications for human health. http://dwi.defra.gov.uk/research/completed-research/reports/DWI70-2-255.pdf
Science Direct. 2019. Paecilomyces. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/paecilomyces
US National Library of Medicine National Institutes of Health. February 2011. Filamentous Fungi in Drinking water, particularly in Relation to Biofilm Formation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3084471/