“Salmonella and other bacteria grow and survive better in sponges than in brushes, the reason for this is that sponges used daily never dry out,” said Trond Mretr, a researcher at Nofima, a Norwegian research institute. eating.
“A single sponge can harbor more bacteria than there are humans on Earth,” said Mretr, author of a new study published online in the Journal of Applied Microbiology.
While many bacteria aren’t harmful, those that are — like salmonella — can spread from sponges to hands, surfaces and kitchen equipment and potentially make people sick, he said. .
“The sponge is wet and accumulates food residue which is also food for bacteria, which leads to rapid growth of bacteria.”
What surprised the researchers most about their findings was that it didn’t matter how well people cleaned their sponges or how often.
“How consumers used their sponges didn’t matter much when it came to bacterial growth. It’s very difficult for consumers to avoid bacterial growth in sponges until the sponges are replaced. daily,” Mretr said.
The research into the sponges and brushes used builds on a lab study published last year by the same team of researchers, which found that harmful bacteria survived better in sponges than in brushes.
In the United States, the USDA has stated that microwaving or boiling kitchen sponges can reduce “some bacterial load”, but these measures alone are not enough to guarantee that your sponge will reduce cross-contamination. He advised buying new ones frequently.
The research was part of a European Union-backed project on food security.
Sponge versus brush
The researchers collected kitchen sponges from 20 people living in Portugal and 35 brushes and 14 sponges from people living in Norway.
An earlier survey of 9,966 people by the research team found that sponges were commonly used to clean kitchens in the majority of the 10 European countries, with brushes being the dominant cleaning utensil for dishes in only two. countries, Norway and Denmark.
The sponges were all used for washing dishes – scrubbing pots and pans, and 19 of Portugal’s 20 sponges were used five to six times a week or more often. Of the brushes collected in Norway, 32 out of 35 were used five to six times a week or more. Sponges collected in Norway were used less frequently.
No pathogenic (disease-causing) bacteria were found in the brushes or sponges. However, overall bacteria levels were lower in used brushes than in sponges. Similar types of non-pathogenic bacteria were found in both cleaning utensils.
When researchers added salmonella bacteria to brushes and sponges, they found a significant reduction in salmonella counts in brushes left to dry overnight. But there was no discount for brushes stored in a plastic bag or for sponges regardless of the storage conditions.
Owners of sponges and brushes explained how long they typically use their sponge or brush and how they keep their cleaning utensils clean – rinsing with water, washing with soap and water, putting in the dishwasher or bleaching.
None of these things made any tangible difference, however, which surprised the researchers. The main conclusion of the study was that the brushes, which dry between uses, contain less bacteria.
“Because the brush dries very quickly, harmful bacteria will die off. Also, most brushes have a handle that prevents you from coming into direct hand contact with potentially harmful bacteria, unlike sponges,” a- he declared.
“I encourage consumers to try a brush instead the next time they need to replace their sponge.”
What to do
While the study authors recommended the bristles of a brush rather than the squish of a sponge, Cath Rees, a professor of microbiology at the University of Nottingham who was not involved in the research, said that she would continue to use a sponge to wash the dishes. For her, the main takeaway was that drying dish sponges and rags between uses was a good idea.
“The main message I get is that they found no evidence of pathogenic bacteria on sponges or brushes collected from various household environments and therefore there is no evidence that these items are a significant source of contamination in normal household environments,” says Rees.
“If there were low levels of pathogens left on your tissue, they’re going to grow quite slowly (they grow best at body temperature), so you wouldn’t expect to see a lot of growth from those- ci, and this was consistent with their results – in wet conditions there was limited growth, in dry conditions the numbers stayed the same or decreased,” she explained.
Markus Egert, a microbiologist at the University of Furtwangen in Germany who conducted similar research, said he already used brushes to wash his dishes, which he cleaned in the dishwasher. If people preferred a sponge, Egert, who was not involved in this study, recommended using a new one every two to three weeks.
“Brushes are the best choice for cleaning dishes, from a hygienic point of view. This could have been anticipated before, but the authors prove it with great experiments. However, in my experience, people love using sponges.”