That kitchen sponge sitting by your sink is not as innocent as it looks. It could be harbouring Salmonella enteritidis, E coli or Staphylococcus aureus – and there’s no way to tell just by looking at it or smelling it.
Author
- Primrose Freestone
Senior Lecturer in Clinical Microbiology, University of Leicester
New research from Germany grew bacteria from sponges in the lab, analysed their DNA and examined them under powerful microscopes. It revealed that food-poisoning bacteria can grow inside everyday kitchen sponges and form sticky, protective layers that are hard to remove. The bacteria could survive for at least two weeks, even once the sponge had dried out.
The researchers also found that germs living in a sponge could transfer to kitchen worktops with a single wipe.
Microbiologists have known for nearly ten years that bacteria from the environment can build up in kitchen sponges, including both harmless types and ones that can cause illness under the right conditions. But this latest study looked specifically at the infection risk.
The researchers found that kitchen sponges may act as a store of germs that can spread bacteria directly on to new surfaces. A contaminated sponge could spread germs elsewhere if used during washing up .
Scientists already understand fairly well how food-poisoning bacteria travel through the food chain before it reaches our homes . But this study could help explain how these infections happen once food is in the kitchen.
Research has shown that bacteria get soaked up into kitchen sponges within just a few minutes of first use. Squeezing out a sponge then releases those soaked-up microbes back into the surrounding environment.
Studying sponges used for different lengths of time – from several days to several months – we found that mould sets in after several weeks of use. We also discovered that disinfecting sponges with bleach becomes less effective the longer they’ve been used. In other words, well-used kitchen sponges may not be fully clean even after a dose of bleach.
Given what the inside of a kitchen sponge is actually like, it’s perhaps not surprising that they’re such a comfortable home for harmful bacteria. Their holey structure means they can hold on to water deep inside even after the surface feels dry, and water is essential for bacteria and mould to survive and grow.
Any food traces left in a sponge also give bacteria most of what they need to multiply . And most kitchen sinks, where sponges tend to live, are warm enough to help along the bacteria that thrive in those conditions .
Sponges are an environmental disaster
Despite being a household staple, kitchen sponges are not popular with environmentalists. Most coloured sponges are made from plastics derived from petroleum.
They’re also hard to recycle, as they’re not biodegradable . And they’ve gained a reputation for shedding significant amounts of microplastic into the environment, prompting a search for alternatives that are being actively sought .
What’s needed, in cleaning terms, are alternatives to the kitchen sponge that are less likely to hold on to bacteria as they’re used. Researchers in Portugal collected used washing-up brushes and sponges from households and compared how much bacteria each carried .
They found that dishwashing brushes dried out faster than sponges. Importantly, brushes also carried far fewer bacteria such as Salmonella on their surfaces.
For those who still favour a sponge, the next question is how to make it safer to use. Avoiding contamination in the first place is the most important step .
Food-poisoning bugs are most commonly linked to raw foods such as meat, poultry and fish, though fruit and vegetables can also carry bacteria and viruses that cause illness . When mopping up blood or spills from raw food, use a paper towel that you can throw away, rather than a sponge, then disinfect the area with an antibacterial spray .
If you’d rather stick with a sponge, the best way to keep bacteria levels down is to spray it with disinfectant periodically throughout the day and swap it for a new one every week. And you might want to consider switching to biodegradable sponges, which are more environmentally friendly .
