Sponges are the dirtiest thing in your kitchen, study finds

You might want to think twice about using a kitchen sponge to clean off your dishes, as a new study published this month in the journal Scientific Reports has found that the objects could be contaminated with a plethora of potentially disease-causing bacteria and other microbes.

As part of their research, Furtwangen University Professor Dr. Markus Egert and his colleagues sequenced the microbial DNA of 14 used kitchen sponges and found high concentrations of such bacteria as Moraxella osloensis, a pathogen that can cause infections in those with weak immune systems and is known for producing a pungent odor, according to Science.

More than 360 different types of bacteria were discovered, including strains related to those that cause pneumonia and meningitis, the study authors explained in a statement. On the plus side, at least fecal bacteria and micobes responsible for causing food poisoning and dysentery were rare.

“What surprised us was that five of the ten which we most commonly found, belong to the so-called risk group 2, which means they are potential pathogens,” Dr. Egert explained, noting that there are 40 million households in Germany. If each had at least one or two kitchen sponges, that means that there could be more than 80 million miniature germ factories in that country alone.

“Sometimes the bacteria achieved a concentration of more than 5 times 1010 cells per cubic centimeter,” he added. “Those are concentrations which one would normally only find in fecal samples. And levels which should never be reached in a kitchen. These high concentrations can be explained by the optimal conditions the bacteria find in the sponge: besides the large surface area for growth, there are high levels of moisture and nutrients from food residue and dirt.”

Forget about sterilizing old kitchen sponges – just buy new ones

No big deal, right? All you have to do is periodically boil or microwave the sponges to sterilize them. Not exactly, the study authors warn: sponges that had been regularly sanitized using these methods were actually found to have a higher percentage of bacteria than uncleaned sponges.

Why? The researchers explained that while boiling or microwaving sponges does indeed result in a short-term decrease in the number of pathogens, those that survive the process become resistant to cleaning attempts, not unlike how gut bacteria become stronger after we take antibiotics.

“Our work demonstrated that kitchen sponges harbor a higher bacterial diversity than previously thought… [and] from a long term perspective, sponge sanitation methods appear not sufficient to effectively reduce the bacterial load in kitchen sponges,” Dr. Egert’s team reported. In fact, they said, such sterilization attempts “might even increase” potentially-harmful bacteria content.

Instead of attempting to boil or microwave sponges, the authors recommend regularly replacing them, perhaps on a weekly basis. This is especially true in places such as hospitals or retirement homes, where patients or residents may have weak immune systems and be more susceptible to such harmful pathogens. No microbial contamination was found in recently bought sponges.