You probably consider your dishwasher a time-saving appliance that makes life easier by doing a dreaded household chore.
But many of the same qualities that make the dishwasher an indispensable cleaning machine -- the moisture, heat, food scraps -- also make it a perfect breeding grounds for fungi, including some that could be harmful to your health.
Researchers collected microbial samples from 189 dishwashers in 18 countries, including Australia, South Africa, China and Slovenia. They were stunned to discover that 62 percent of the dishwashers tested positive for fungi. And 56 percent had a fungal species known as Exophiala, a kind of black yeast that looks like black slime.
"We were surprised to find some fungi that are extremely rare in nature but had really high numbers in dishwashers," says Nina Gunde-Cimerman, a professor of microbiology at the University of Ljubljana in Slovenia.
The study, published in the journal Fungal Biology, focused on the fungi found by swabbing the rubber seals of dishwasher doors, an area these organisms can degrade and hide within.
Two kinds of Exophiala species were seen and even the microbiologists were amazed they withstood the high heat, detergents, and salt concentrations found inside dishwashers. Cimerman suspects the fungi arrived via tap water, and the hardness of water also seems to play a role.
Exophiala is known to colonize on the lungs of patients with cystic fibrosis. It may sometimes cause fatal infections in healthy people, too.
Researchers warn that "the invasion of black yeasts into our homes represent a potential health risk." Their presence on plates or forks, for example, may spread infections even though none were reported in the sampled households. Only further study can determine if these dishwasher fungi can be dangerous to human health.
Until then, clean any disgusting black slime off the seal of your dishwasher.