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Updated Sep 04, 2017 @ 10:00 am
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If you’ve been mulling over whether or not it’s time to buy a dishwasher, here’s the information that could put you over the edge: there are 54 billion bacterial cells on a single cubic centimeter of the average kitchen sponge.

You might already know that it’s your kitchen, not your bathroom, that has the most microbial activity, and that’s indeed because of your sponge—"the biggest reservoirs of active bacteria in the whole house.” But did you know that cleaning your sponge only makes things worse?

In a recent study published in the journal Scientific Reports, researchers in Germany found that used kitchen sponges were home to dozens of bacterial microorganisms (the researchers charted just the top 20 bacteria), and out of the top 10 most abundant bacteria, five were closely related to those classified as RG2, microbes associated with preventable human illnesses including food poisoning. The testing size was relatively small (14 sponges, separated by top and bottom into 28 samples), but the 10 most common bacteria were “quite ubiquitous,” the study notes.

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What’s more, the samples taken from homes where they had been “regularly cleaned,” according to their owners, were even worse. In those sponges, two of the 10 most common RG2 bacteria, Chryseobacterium hominis and Moraxella osloensis, were found in “significantly greater proportions.”

“From a long-term perspective,” the researchers wrote, “sponge sanitation methods appear not sufficient to effectively reduce the bacterial load in kitchen sponges and might even increase the shares of RG2-related bacteria.”

And because kitchen sponges typically get used for multiple tasks (not just cleaning dishes, but wiping countertops and any number of surfaces), our sponges aren’t just a “reservoir of microorganisms,” the team writes, “but also as disseminators over domestic surfaces, which can lead to cross–contamination of hands and food, which is considered a main cause of foodborne disease outbreaks.” In other words, your sponge is really good at spreading bacteria all over your kitchen.

So what’s a conscientious (and now completely grossed-out) household to do? Well, you’ll be happy, and not that surprised, to learn that “notably, no bacteria could be detected in a collection of newly bought, i.e. unused kitchen sponges.” Since it’s run-of-the-mill kitchen activities that bring these bacterial colonies to life, the researchers suggest that we replace our sponges weekly.

Though the team notes that more work needs to be done to measure the actual pathogenicity of the used kitchen sponge—that is, how are these sponges actually making us sick?— I feel comfortable saying that we should all just start fresh with a new sponge today, and start buying them in bulk.

If you want to get a much closer look at what’s living in your kitchen sponge, read the full study here.