Harmful fungi found in dishwashers
MedWire News: Dishwashers play host to several strains of extremotolerant fungi that may be hazardous to human health, study findings indicate.
The researchers, led by Polona Zalar (University of Ljubljana, Slovenia), isolated 22 different types of fungi and yeast from 102 household dishwashers in Slovenia and from 87 dishwashers in homes in several other countries worldwide.
They explain that dishwashers share a number of characteristics with certain fungi-friendly wet indoor environments, such as kitchens and bathrooms. These include continuous moisture, high pH due to the regular use of detergents, temporarily increased temperatures, and high amounts of organic matter.
The team collected samples from the rubber door seals on dishwashers of different ages (6 months to 15 years), with different frequency of usage (once per month to 3 times per day).
They reveal in the journal Fungal Biology that 65% of the dishwashers were positive for fungi. The black yeast Exophiala dermatitidis and E. phaeomuriformis (Chaetothyriales) accounted for 56% of the organisms isolated.
Species belonging to the genera Aspergillus, Candida, Magnusiomyces, Fusarium, Penicillium, and Rhodotorula were also identified, but were less common.
"The high prevalence of the two Exophiala species can be explained by their remarkable thermotolerance, halotolerance and pH tolerance, the combination of which has previously not been observed in fungi," Zalar et al remark.
Indeed, laboratory testing showed that the Exophiala species grew at temperatures up to 47°C, in a pH range between 2.5 and 12.5, and with up to 17% NaCl salinity.
The researchers note that both Exophiala species are known to cause systemic disease in humans, and frequently colonize the lungs of patients with cystic fibrosis.
"Knowing that these fungi co-inhabit our homes, further research is imperative, as only this could reveal whether the presence of Exophiala inside our households poses any threat to human health," they write.
They add that special attention should be paid to dishwashers in hospital wards with immunocompromised patients.
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By Laura Dean