The most bacteria-infested item in your house may not be in your bathroom.
It may be in your kitchen.
Even an attempt at cleaning them doesn’t do much good, researchers said.
Since sponges are porous and often wet, bacteria can happily colonize this common cleaning device.
Understanding the microbiome around us
The study authors, based in Germany, pointed out that today most humans spend about 90 percent of their time in “built environments,” which are full of a variety of bacteria called a “microbiome.”
Understanding what is growing in our kitchen sponges can be key in understanding how our health is impacted in this microbiome.
“Due to continuous mutual interactions, the [built environment] microbiome is suspected to have a significant impact on health and well-being of the human occupants, which probably goes beyond classical infectious diseases, such as food-borne illnesses,” the authors wrote. “However, the details are far from being fully understood.”
Dr. Amy Edwards, an infectious disease physician with University Hospitals Cleveland Medical Center, said that studies like this can shed a light on what threats we actually face from bacteria, which is naturally abundant in the world around us.
“We know that we’re surrounded by bacteria, but what does that mean?,” she told Healthline.
Just because bacteria are all around us, “That doesn't mean you should go around licking raw chicken,” she said.
In order to understand the components of this microbiome, the researchers from Germany looked at the bacterial makeup of 14 used kitchen sponges. They used special scans that looked for bacterial DNA in the sponge.
Not surprisingly, they found a host of bacteria within the sponges. The most abundant classes of bacteria included Gammaproteobacteria, Pseudomonadales, and Flavobacteriales.
While the bacteria that were prominent in the findings are not usually as infectious or dangerous as others like salmonella or E. coli, they can present a risk for people with compromised immune systems.
“It's reassuring that most of us aren't going to get sick from Acinetobacter,” Edwards explained of one common phyla of bacteria found in the sponges. “But certainly someone who is on chemotherapy can.”
Forget cleaning the sponge.
The researchers also found that cleaning sponges by boiling or microwaving them didn’t do much to rid them of bacteria.
“Our data showed that regularly sanitized sponges (as indicated by their users) did not contain less bacteria than uncleaned ones,” the authors wrote.
They found special cleaning even increased some numbers of certain bacteria.
The authors wrote that when sponges are cleaned by boiling or microwaving them, some hardy bacteria remain behind and can quickly recolonize the sponge.
The sponges were not colonized with bacteria when they were new.
While extremely pathogenic bacteria were not found in high numbers, Edwards said the study makes her wary about using kitchen sponges to clean items that might contain harmful bacteria.
“When you drop the raw chicken to the countertop… you're going to grab something to clean that up,” said Edwards. “You rinse it out under the water as if rising it” disinfects it.
Using a sponge now colonized with salmonella to clean dishes could cause food-borne illnesses.
Edwards said she wasn’t surprised that bacteria can survive cleaning attempts.
“They're a latticework for fibers,” Edwards said of sponges. “It’s too easy for bacteria to hide in the crevices.”
She said people could try dunking the sponges into bleach or vinegar solution, but she’d suggests just throwing them out.
Edwards said since working in the infectious disease field she has already stopped using sponges entirely, and now sticks to dish clothes that she throws out every few days.
If you’re ready to switch to all paper plates and paper towels, don’t give up just yet.
The researchers advise throwing out your kitchen sponge on a regular schedule, around once a week, to discourage any possible spread of dangerous bacteria from sponge to your dinner plate.