Hidden dangers of the dishwasher

Not only do dishwashers and washing machines leave your dishes and clothes sparkling clean, they also create the ideal conditions for pathogenic fungus to grow

Researchers took samples from the rubber band door of 189 dishwashers from private homes in 101 cities in six continents. The dishwashers ranged from 6 months to 15 years old, and varied in their usage, from once a month to three times a day.

“Dishwashers combine high temperature, high alkalinity, high salinity and high organic load – therefore they appeared as perfect extreme places for pathogens to develop,” Professor Nina Gunde-Cimerman from the University of Ljubljana told Laboratory News.

Gunde-Cimerman’s group were the first to discover extremophilic fungi in hypersaline water and Arctic glaciers, and turned their attention to look for extremophiles in domestic habitats – and found them, publishing the results in Fungal Biology.

Using molecular methods and scanning electron microscopy, they discovered 62% of samples tested positive for potentially pathogenic fungal flora – of this, 56% contained polyextremotolerant black yeasts Exophiala dermatitidis and E. phaeomuriformis.

Moist and hot environments are characteristic of dishwashers and washing machines, and both strains of Exophilia showed remarkable tolerance to the high heats – temperatures between 60°C and 80°C are produced intermittently in a dishwashing cycle – and withstood high salt concentrations, aggressive detergents and tolerated both acidic and alkaline water. This combination of extreme properties has not been observed in fungi before.

The invasion of these black yeasts in our household appliances represents a potential health risk, even for the most healthy of people. E. dermatitidis is rarely isolated from nature, but is frequently encountered as an agent of human disease in both compromised and healthy people. It is involved in pulmonary colonisation of patients with cystic fibrosis and occasionally causes fatal infections in healthy humans.

The discovery of this widespread presence of extremophilic fungi in common household appliances like washing machines, dishwashers, even the coffee machine, suggests these fungi have evolved and could pose a significant risk to human health in the future. The fungi have occasionally been isolated from saunas, but getting rid of them required more research, said Gunde-Cimerman.

Dishwashers – A man-made ecological niche accommodating human opportunistic fungal pathogens www.elsevier.com/locate/funbio