Kitchen sponges have way more bacteria than you think

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Sponges, an everyday item found in kitchens around the world, are an ideal breeding ground for bacteria, according to a new study. Researchers have found that sponges can host around 54 million bacteria per cubic centimeter thanks to their optimal physical properties for bacteria: airy, moist and full of food scraps.

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Bacteria have different ways of interacting with living things such as humans. Some bacteria are more social, while others prefer to be alone. A group of Duke University researchers wondered how separating different types of bacteria would affect these interactions. They found that balanced separation levels are the best choice for most types of bacteria – and that’s exactly what they get in a sponge.

The sponges are divided into sectors of different sizes, which satisfies bacteria that prefer an isolated environment as well as those that want to be around other organisms. So a sponge really is the best of both worlds for microbial communities.

Researchers have found that bacteria that grow in small spaces, such as the small pores of a sponge, won’t bother other organisms for more space, while the sponge’s larger surface areas allow microbes who depend on others to be there to survive. If you combine this with food scraps from a sponge, it becomes an ideal place for bacteria.

“Bacteria are like people living through the pandemic – some struggle to isolate themselves while others thrive,” Lingchong You, the study’s author, said in a statement. “We demonstrated that in a complex community that has positive and negative species interactions, there is an intermediate amount of integration that will maximize its overall coexistence.”

Sponges and bacteria

The researchers barcoded a group of strains of E.coli to follow their population growth. They mixed the bacteria in different combinations on laboratory growth plates with a variety of potential living spaces, from six to over 1,500 small wells. Large wells allowed bacteria to mix freely, while in small ones they could stay together.

Small wells that started with a group of species evolved into a community with only one or two surviving strains. Similarly, larger wells that started with a wide range of bacteria also ended up with only one or two species. The researchers also did a similar experiment with a sponge and discovered a much more diverse bacterial environment.

“The small portions really hurt species that depend on interactions with other species to survive, while the large portions eliminated members that suffer from these interactions (solitaries),” You said in a statement. “But intermediate portioning allowed for maximum diversity of survivors in the microbial community.”

Researchers advise people to be mindful and periodically change their sponges or at least find a way to clean them. A 2017 study recommended replacing sponges on a weekly basis. Yes, you read well, every week. If you want to clean it, the US government suggests using microwave heating and dish washing with a drying cycle.

The study was published in the journal Nature.

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