Your Dishwasher Is Not as Sterile as You Think

From Drugs.com - January 12, 2018

Your Dishwasher Is Not as Sterile as You Think

FRIDAY, Jan. 12, 2018 -- Your dishwasher may get those plates spotless, but it is also probably teeming with bacteria and fungus, a new study suggests.

Microbes -- from bacteria to viruses to fungi -- are everywhere, including within and on the human body. So it's no surprise, the researchers said, that a kitchen appliance would be hosting them.

So do people need to worry about getting sick from their dishwashers? No, said Erica Hartmann, an assistant professor at Northwestern University who was not involved with the study.

"The risk is probably in the realm of a shark attack," she said. That is, most people face little to no risk, but there are select groups who may be at higher risk -- in this case, people with conditions that weaken their immune defenses.

Dishwashers are an interesting case when it comes to microbes because they are actually an "extreme" habitat, Hartmann explained.

"People do not think of them that way. It's just your dishwasher. But it really is an extreme environment," said Hartmann, who studies the microbiology of the indoor environment.

Dishwashers create constantly fluctuating conditions -- wet to dry, high heat to cooler temperatures, low to high acidity. They also harbor mixtures of detergents and dinner scraps. So, only certain microbes will thrive.

The new study looked at which bacteria and fungi are actually dwelling there, and what factors seem to influence that microbial makeup.

Specifically, the European researchers took samples from the rubber seals of 24 household dishwashers.

Overall, they found, the most common bacteria included Pseudomonas, Escherichia and Acinetobacter -- all of which have strains that are "opportunistic pathogens." That means they are normally harmless, but can cause infections in people with a compromised immune system.

The most common types of fungus were Candida, Cryptococcus and Rhodotorula -- which also include opportunistic pathogens.

Nina Gunde-Cimerman, a professor of microbiology at the University of Ljubljana, in Slovenia, worked on the study.

She said dishwashers and other microbe-hosting appliances are "generally safe" for healthy people. It's "sensitive groups," she said, who may need to be more cautious.

Gunde-Cimerman said she and her colleagues suspect dishwashers might play a role in fungal infections called mycoses in certain immune-compromised patients. A fungus commonly found in those patients, she said, is known as Exophiala dermatitidis, or black yeast.

And while that fungus is "hardly known in nature," she said, it's easy to find in dishwashers.

However, Gunde-Cimerman stressed, that's speculation. No one has yet proven a connection between dishwasher microbes and mycoses infections.


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