Kitchen sponges are notorious for being bacteria-ridden. By some estimates, they are dirtier than toilet seats. Strains of germs range from campylobacter, salmonella, and staphylococcus to E. coli and listeria.
"That thing is very dirty," Philip Tierno, a microbiologist and pathologist at the New York University School of Medicine, tells Tech Insider. "Mainly because you're cleaning up vegetables, carcasses of meat, and all sorts of food stuff that can potentially contain pathogenic [disease-causing] bacteria that will grow in numbers over time."
If you're part of the camp that believes microwaving your kitchen sponge will kill all the bacteria, then Germany researchers have some bad news: While the microwave will terminate weaker bacteria, it has no effect on stronger species.
The scientists, who published their findings last month in the journal Scientific Reports, studied the DNA and RNA in 14 sponge samples to find 362 different variations of bacteria. What's more, bacteria is concentrated: One cubic inch of sponge space is home to 82 billion bacteria.
"That's the same density of bacteria you can find in human stool samples," Markus Egert, a microbiologist at the University of Furtwangen and lead researcher of the study, tells The New York Times. "There are probably no other places on earth with such high bacterial densities."
Even more alarming is the discovery that disinfecting sponges leaves you no better off than letting them be dirty. In fact, the researchers found more "potentially pathogenic bacteria" in sponges that were regularly cleaned.
"Presumably, resistant bacteria survive the sanitation process and rapidly re–colonise the released niches until reaching a similar abundance as before the treatment," the team writes.
The solution, says Egert, is to replace your kitchen sponge on a weekly basis. Yes, that's probably way more often then you're use to. It's not the greatest alternative when you take the environment into consideration, but it does keep you relatively safer from bacteria.