The situation isn't as bad as it sounds, but still, researchers' finding about a kitchen staple would give anyone who draws dish duty pause. "A single sponge can harbor a higher number of bacteria than there are people on Earth," said Trond Møretrø, a research scientist at a Norwegian food research institute, per CNN. Møretrø is an author of a new study in the Journal of Applied Microbiology about bacteria levels in kitchen sponges and brushes. "Salmonella and other bacteria grow and survive better in sponges than in brushes; the reason is that sponges in daily use never dry up," he said.
Many of those bacteria are not harmful. But the ones that are, including salmonella, can spread from the sponges to kitchen surfaces, equipment, and hands, Møretrø said, possibly making people ill. Moisture is an issue, as is the fact that the sponges collect food residues that feed bacteria, he said. The findings showed that cleaning the sponges didn't make much difference. The US Agriculture Department suggests buying a new sponge often, saying that microwaving or boiling a sponge being used has limited effect in killing bacteria.
The study recommends using a kitchen brush, which usually holds onto lesser amounts of bacteria, instead; the bristles of a brush dry out between uses.
Other experts were less worried, per CNN. A microbiology professor in England said the study didn't find much danger in the bacteria in sponges, so she doesn't plan to switch to a brush. But Cath Rees endorsed the idea of drying out the sponge or brush between uses. A microbiologist in Germany who also has researched the issue said he uses a brush, then puts it in the dishwasher. The study's authors, he said, demonstrate "with some nice experiments" that brushes are more hygienic. Still, Markus Egert said, "People love using sponges."