Harmful bugs can thrive in your kitchen sponge for weeks – and you won’t be able to tell

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.

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 10 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.