No matter how often you replace your kitchen sponge, it will always be a friendly environment for bacteria.
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hand washing dishes with sponge
Credit: Nattakorn Maneerat / Getty Images

Do you use a sponge to wash your dishes? If so, how often do you replace it? A new study conducted by researchers from Duke University revealed that the average kitchen sponge has more bacterial species than a lab petri dish. Even more shocking, the bacteria doesn't come from dirt and grime, but rather it's the structure of the sponge that makes it a habitable place for microbes to reside. This means that no matter how often you replace you sponge, it will always be a friendly place for unwelcome germs.

The researchers identified and barcoded about 80 different E. coli strains so they could track their population growth. Then they mixed the bacteria in various combinations on laboratory growth plates with a wide variety of potential living spaces ranging from six large wells to 1,536 tiny wells. The large wells approximated environments in which microbial species can mix freely, while the small wells mimicked spaces where species could keep to themselves. No matter the habitat size, the results were the same. The small wells that started with multiple species evolved into a community with only one or two strains survivingthe same goes for the large wells that began with a range of species.

According to Lingchong You, professor of biomedical engineering at Duke, the results "create a framework for researchers working with diverse bacterial communities to begin testing what structural environments might work best for their pursuits." The team's findings also point toward why a kitchen sponge is such a healthy habitat for bacteria. When the researchers ran their experiment using a strip from a regular household sponge, they found it was an even better incubator of microbial diversity than the lab equipment they tested.

This is because, like humans, some bacterial species prefer to live with their fellow germs, while others like to be alone. In this study, researchers found bacterial species that prefer a "mixed-housing environment" were more likely to live in your kitchen sponge, as it provides different layers of separation combined with various sizes of communal spaces. "As it turns out, a sponge is a very simple way to implement multilevel portioning to enhance the overall microbial community," says You. "Maybe that's why it's a really dirty thing—the structure of a sponge just makes a perfect home for microbes." The results suggest that structural environments should be considered by industries that hope to use bacteria to accomplish tasks in the future, such as cleaning up pollution.

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