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SALT LAKE CITY -- Two Utah communities were included in a worldwide study on pathogenic molds, published in Britain this summer.
Researchers took samples from the rubber seals of home dishwashers in 101 communities. The majority of the samples came from Europe via researchers at the University of Ljubljana in Slovenia. The study later expanded to include samples from North and South America, Israel, South Africa, Far East Asia and Australia. The six U.S. samples, which all tested positive for fungi, came from Placerville, Calif., and two from Utah – Salt Lake City and Arches.
Both Utah samples tested positive but for different genotypes. The Salt Lake City sample was positive for Exophiala dermatitidis and the Arches sample for the black yeasts Exophiala phaeomuriformis.
The study, “Dishwashers—A man-made ecological niche accommodating human opportunistic fungal pathogens,” was authored by P. Zalar, M. Novak, G.S. de Hoog and N. Gunde-Cimerman. It was published in June in “Fungal Biology,” a journal of the British Mycological Society.
The study emphasizes “...there have been no reports on the infection of healthy humans in households using dishwashers but the potential hazard they represent should not be overlooked.”
It is of interest that fungi that we know as hospital infections reside with small amounts in what we call pioneer situations - rather extreme, low in nutrients, and with not much competition of other microbes.
–G.S. de Hoog
The intent of the study was not “to scare people with dangerous fungi in your household,” said de Hoog, one of the principle researchers and a professor at universities in Amsterdam, Beijing and Guangzhou. “These fungi occur worldwide and apparently are very common. They occur in Salt Lake City just as anywhere else. But there is no danger at all for normal individuals; the number of infections is very small, even in immunocompromised.”
The study, funded by the Netherlands government, reports the discovery of this widespread presence of heat tolerant fungi in common household appliances and suggests these organisms have mutated and evolved in a process that could pose a risk to human health in the future.
“It is of interest that fungi that we know as hospital infections reside with small amounts in what we call pioneer situations – rather extreme, low in nutrients, and with not much competition of other microbes,” de Hoog said.
A pioneer situation occurs when a fungus survives despite unfavorable conditions.
The researchers were surprised in the study that the fungi thrive in near boiling temperatures and dry heat and seems to be protected by the rubber seals in highly alkaline conditions as high as 12.5 pH. The colonizations were greater with hard water situations. However, in some of the samples, that data was unavailable to researchers.
“Weekly cleaning (the doors and seals) with normal household detergents like Cif seems OK,” de Hoog said.
Cif is a cleaning product made by Unilever and is intended to replace normally abrasive powder cleaning products such as Ajax and Comet. It is not sold in the U.S. but a similar non-abrasive product could be used. People need to a clean on a regular basis because the rubber seal of a dishwasher is a “preferred habitat” and the fungi will return, de Hoog said.
62% of the dishwashers tested positive for the fungus genus, Aspergilla, and 56% tested positive for Exophiala - including the Salt Lake City sample.
Dishwashers are the most likely appliance in the home for fungus growth and human contamination although the study suggests washing machines may be a niche environment for fungal growth, and de Hoog said there needs to be more research. Dishwashers pose the most risk because they provide nutrient rich food sources. For example, human food is on dirty dishes, providing nutrients for fungus growth.
“A dishwashing cycle also produces high salt and alkaline conditions, with intermittent high temperatures and large amounts of water which does not seem to have adversely affected their growth,” according to the study. “The fungus has been able to adapt to these extreme conditions and still thrive.”
The study said part of the problem may be the result of energy-saving regimens such as the lower temperatures for washing clothes and dishes and the increased use of less aggressive detergents designed to have low impacts on the environment. The study implies that green practices and products could be having a detrimental effect when considering fungal pathogens affecting human health, but the risk is minimal.
In the study, 62 percent of the dishwashers tested positive for the fungus genus, Aspergilla, and 56 percent tested positive for Exophiala – including the Salt Lake City sample – a bacteria that colonizes the lungs of people with cystic fibrosis or compromised immune systems, usually in hospitals and health care institutions. Usually these infections are below skin in deep tissue. Other bacterial funguses identified were Candida, Magnusiomyces, Fusarium, Penicillium and Rhodotorula, which were reported only occasionally. However, the black yeasts Exophiala dermatitidis and Exophiala phaeomuriformis were frequently isolated. In some cases more than one fungus was identified in the same place or nearby.
Molds and allergens are common, existing almost everywhere and unavoidable to most people. In many cases they are airborne and invisible to the naked eye. According to the authors, other scientists have traditionally focused mostly on airborne fungal pathogens, and there is a vast amount of research on airborne fungal flora in our homes, especially Aspergilla fumigatus because of the possibility of human health problems.
There are a growing number of electric appliances that use rubber seals and water, all of which could be considered ecological niches suitable for fungal growth, according to the researchers. One caveat is all of those appliances probably do not provide nutrient rich environments to the same extent as dishwashers. Places in homes that are of increasing concern are wet locations such as bathrooms, kitchens, saunas and electric appliances that use water.
Mel Borup Chandler is a former Utah resident who lives in California. He writes on pest control and science topics of interest. He works in real estate in the multi-family housing sector of the industry. His email is mbccomentator@roadrunner.com.
