Think Fungus: Washing the Dishes

Dishwashers are very good at creating the conditions that will clean plates and pans. The interiors of dishwashers in use are high temperature, moist, alkaline places that are very good at removing grease and grime but are they effective at removing bacteria and fungi from your cutlery? For the most part they great conditions for cleaning but for a few microbes they are also excellent conditions for growth.

Two studies, one in 2011 and another in 2012  took samples from hundreds of household dishwashers from homes in Europe, Asia, the Middle East, Africa, Australia, and North and South America. They also took samples from lots of other potential microbial growth ‘hot spots’ for example shower heads, baths, and washing machines but it was the dishwashers that gave the most concern.

In the first study 62% of all dishwashers were found to be positive for fungal growth including  Aspergillus,  Candida,  MagnusiomycesFusariumPenicillium and Rhodotorula were found occasionally, while the black yeasts Exophiala dermatitidis and Exophiala phaeomuriformis (Chaetothyriales) were persistently and most frequently isolated.

In the second study 30 samples out of 893 were positive for several different fungi. Exophiala dermatitidis was the most common species (23), followed by E. phaeomuriformis (three), Magnusiomyces capitatus (two), and Candida parapsilosis (two). It turns out that your dishwasher is a terrific place for black yeasts to grow.

Many of these species are known to be pathogenic to humans and cause disease, for example Exophiala is known to infect humans and cause systemic disease, some species of Aspergillus causes aspergillosis, an incurable lung infection that affects millions of people worldwide.

Dishwashers that are not sufficiently and regularly cleaned particularly around the rubber door seals are prone to supporting the growth of many pathogenic species of fungi. The authors suggest that presence of reservoirs of these pathogens in many of our homes may be one route that can lead to infection. Further research is strongly suggested.