The kitchen sponge.
Scientists have confirmed that no, the toilet is not the dirtiest household item in terms of the presence of bacteria. It's actually the kitchen sponge, which we use to scrub utensils or wipe down kitchen surfaces.
Of course, if you think about it, these findings aren't really surprising. The toilet may be where we do less savory things, but a sponge is a more likely place where microbes can thrive. After all, it's damp most—if not all—of the time, it's full of food particles, and it has a porous structure. It's a great breeding ground and reservoir for live bacteria. In fact—let's go back to the toilet for a second—a sponge can have just as many bacteria as can be found in fecal matter. Scientists say that the bacteria in a sponge should never reach the levels of fecal bacteria, but it can happen.
So just how germy is a kitchen sponge?
Researchers at Furtwangen University in Germany tested 14 used kitchen sponges. They ran genetic sequencing on the sponges to find out how many bacteria reside in the springy, porous material. According to the findings, there's a total of 362 types of bacteria just chilling out in the dirtiest household item we can find. There can be up to 54 billion bacteria cells per cubic centimeter. That's quite the diverse microbiome.
The researchers also used a technique called fluorescence in situ hybridization with confocal laser scanning microscopy (FISH-CLSM) to create 3D visualizations of bacteria on a sponge.
And now for the good news: the majority of these bacteria is not actually harmful. This is something we don't really think about—and something we'd probably prefer not to think about—but bacteria are everywhere. In fact, scientists say that we have as many bacteria cells on our body as we do skin cells.
However, some types of bacteria on sponges are actually harmful. Researchers found five types that can be potential pathogens—Acinetobacter johnsonii, Moraxella osloensis, Chryseobacterium hominis, Acinetobacter pittii and Acinetobacter ursingii. Bacteria in the Moraxellaceae family were the most common in sponges. Interestingly, Moraxellaceae is also commonly found on human skin. This indicates that we may actually be the ones giving sponges the most bacteria.
Sponges can also spread bacteria to the surfaces they touch. These surfaces include appliances, countertops, and whatever else we “clean” with a sponge. This can lead to cross-contamination, which in turn can lead to food-borne diseases.
What, therefore, can we do to avoid spreading bacteria around in our kitchen and on our skin? Sanitizing sponges isn't the way to do it, say the researchers. If we, for example, boil sponges in water or microwave them to kill bacteria, we'll actually just be making the bacteria stronger. The researchers say that we have one week before a kitchen sponge turns into the dirtiest household item you can touch. So, here's a relevant question: when was the last time you replaced your kitchen sponge?
Get weekly science updates in your inbox!