And among those taking advantage of these amenities, the scientists found, was a microbe called Moraxella osloensis. It is widespread in nature and lives on the human skin. It can cause infections in people with weak immune systems, although the risk posed by the bacteria found in sponges is hard to assess.
Moraxella osloensis is primarily responsible for the stench of dirty laundry, and it may also be the reason that your sponge eventually emits a funky odor.
The odor is a compound produced by the bacterium’s metabolism. It eats fat. It excretes fat. And that fatty excrement stinks.
The thrifty among us may try to clean a sponge that starts to stink, but it’s probably time to let it go. Disinfecting it, as many have tried, does not necessarily work. You can microwave a sponge, throw it in the laundry or dishwasher, douse it in vinegar or other cleansing solutions or even cook it in a pot. But the researchers discovered more of the potentially pathogenic bacteria, like Moraxella osloensis, on the sponges collected from people who said they routinely disinfected them.
“When people at home try to clean their sponges, they make it worse,” Dr. Egert said — similar to how people can encourage antibiotic resistant bacteria if they don’t follow the doctor’s orders. He says if you can’t clean it perfectly, it may be best to replace it with a new one every week or so — especially “if it starts to move.”
But if you would rather not create that much waste, run it through a laundry machine at the hottest setting using a powder detergent and bleach and then use it somewhere other than the kitchen that is less hygiene-sensitive, like the bathroom.
“Now I’m an expert in how to clean sponges,” said Dr. Egert, who wants to compare disinfection methods in a follow-up study. “I’m waiting for the sponge industry to call me.”