Your Kitchen Sponge Is Dirtier Than Your Toilet, Study Finds

Do you replace your kitchen sponge every week? If not, then you might want to consider doing so, according to reports Tuesday citing a new study published online in July in the journal Scientific Reports.

A German group of researchers, from the Faculty of Medical and Life Sciences, Institute of Precision Medicine (IPM), Microbiology and Hygiene Group, Furtwangen University, conducted a DNA analysis of kitchen sponges and found 362 kinds of bacteria. The researchers said their study revealed "an amazing bacterial colonization of kitchen sponges, and visualized its extent for this common microbial hot spot for the first time."

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Researchers at the university analyzed 14 different kitchen sponges and found that they harbor even more bacteria when compared to a toilet. Sponges are mostly moist and designed for absorption and thus have the potential to pick up bacteria like salmonella, E. coli, and staphylococcus while you clean your utensils and kitchen counters.

In order to conduct the study, researchers used a method called DNA pyrosequencing to sequence the DNA of 28 samples of bacteria collected from 14 different kitchen sponges taken from private households in Baden-Württemberg, Germany.

They discovered 118 genera of bacteria, most of which were not harmful. However, there were pathogens that could cause infections among humans. Sponges are also capable of spreading bacteria in places where it was not previously present.

"Despite common misconception, it was demonstrated that kitchen environments host more microbes than toilets. This was mainly due to the contribution of kitchen sponges, which were proven to represent the biggest reservoirs of active bacteria in the whole house," the study said.

The researchers also said that "kitchen sponges not only act as a reservoir of microorganisms, but also as disseminators over domestic surfaces, which can lead to cross-contamination of hands and food, which is considered a main cause if food-borne disease outbreaks."

"Kitchen sponges are likely to collect, incubate and spread bacteria from and back onto kitchen surfaces, from where they might eventually find their way into the human body, e.g. via the human hands or contaminated food," the study said.

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The conventional methods for cleaning your kitchen sponges include soaking the sponge in water and putting it in the microwave for over a minute or more than two minutes. The microwave will kill the bacteria by heating the water in the sponge. Another way to clean it would be to soak it in a bleach solution for five minutes or use products consisting of hydrogen peroxide, isopropyl alcohol, ammonia or vinegar — all of which have been proved to kill 99.9 percent of bacteria, according to the Public Health and Safety Organization.

The remaining 1 percent bacteria will remain in your kitchen sponges.

Researchers also found microwaving a sponge only kills about 60 percent of the bacteria and some might even increase after cleaning as the resistant bacteria survives the cleaning process and then re-colonizes again.

The researchers also used a separate method called fluorescence in situ hybridization "which uses fluorescent probes that bind to specific parts of DNA - coupled with confocal laser scanning microscopy, to visualize a close-up image of the bacteria within the sponge."

They also came to the conclusion that cleaned sponges contain almost an equal amount of bacteria as unclean ones.

"Our data showed that regularly sanitized sponges (as indicated by their users) did not contain less bacteria than uncleaned ones," the researchers wrote in the study. "Presumably, resistant bacteria survive the sanitation process and rapidly re-colonize the released niches until reaching a similar abundance as before the treatment."

The researchers concluded the study with the suggestion of replacing sponges weekly instead of doing it monthly.