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Kitchen sponges are teeming with microbes, and microwaving them or washing them in hot water doesn't work to kill those germs. A new study by researchers in Germany took samples from 14 used kitchen sponges and extracted genetic material to identify and sequence the microbes.
Here & Now's Jeremy Hobson talks with Massimiliano Cardinale, one of the authors of the study.
On how full of microbes used kitchen sponges are
"Really full, really full more than we expected. Basically, the sponge can be seen as a complex habitat where several microbes live in. We concentrated our study on bacteria, because from the diversity point of view the bacteria are the most interesting, and from the metabolic point of view, they are also the more rich. And also, because they might represent a threat for humans, because, as you know, there are a lot of good bacteria, but also a few quite nasty ones."
On what types of bacteria live on your sponge
"Actually, we thought that we would detect typical pathogens like salmonella, or campylobacter, but what we found was really surprising: We could not even detect this kind of bacteria, but we found a really massive contamination by another category called opportunistic pathogens. These are species which are usually not dangerous for healthy people, but they might cause infections and diseases in people with a compromised or a weak immune system."
On whether using antibacterial soap to clean your sponge makes a difference
"We observed that it does not really help, and we explained this because such bacteria are very resistant to stress conditions. This is what makes them also dangerous for us, and this means that when people try to disinfect or sanitize the sponge at home, what they are really doing is selecting the most resistant bacteria that will survive, and after that, they will fast colonize the sponge again."
On whether microwaving your sponge or cleaning it in the dishwasher can help
"In our study, we had sponges that were cleaned with special products, we had sponges that were regularly treated by microwave radiation, and we could not find a difference in the amount of bacteria. But, concerning the type of bacteria, we found that the regularly sanitized sponges had more opportunistic pathogens. So it could be even worse — not only it doesn't help."
On possible solutions
"A used sponge is not the most appropriate tool to clean the dishes, perhaps a dishwasher is better. ... Probably, it's better to have a replacement rate which is a little bit more frequent. I would avoid [keeping] a sponge longer than 10 days."
This segment aired on August 8, 2017.