Kitchen sponges should be replaced daily, microbiologist warns — E. coli, salmonella multiply rapidly

Even a small number of bacteria on a kitchen sponge can multiply rapidly, research has found. Experts advise replacing sponges after a single day's use to reduce the risk of food poisoning.

According to the Daily Mail on Saturday (local time), Dr. Primrose Freestone, an associate professor of clinical microbiology at the University of Leicester, warned that using a sponge too long risks spreading food-poisoning bacteria to dishes. "Kitchen sponges are best used for just one day," she said.

"Sponges absorb bacteria very quickly," Freestone said. "Food debris and moisture inside the sponge serve as nutrients, allowing bacteria to multiply over time."

Germany's Federal Institute for Risk Assessment (BfR) recently confirmed that harmful pathogens — including E. coli, salmonella and Staphylococcus aureus — can multiply rapidly even when present in small quantities on a sponge.

When the pathogens were cultured on sterile sponges and examined under high-powered microscopes, E. coli and salmonella showed marked growth within just a few days. Staphylococcus aureus multiplied more slowly than the other pathogens but was detected throughout the entire observation period.

The pathogens also survived for up to two weeks even after the sponge had dried out completely. Researchers said the sponge's porous structure, combined with trapped moisture and food debris, creates an ideal environment for microbial growth.

Sponges also act as a vehicle for spreading bacteria to other surfaces. Wiping a countertop just once with a contaminated sponge can transfer up to 100,000 colony-forming units of bacteria onto the surface.

Notably, no discoloration or odor appeared on the sponges even when food-poisoning bacteria were present in high concentrations — meaning a sponge that looks clean may already harbor billions of bacteria.

"If a sponge smells bad, it usually means microbes have multiplied to a serious degree," Freestone said. "You should never use such a sponge to wipe countertops or wash pots."

However, daily replacement is not always practical. The BfR recommends replacing a sponge immediately after handling raw chicken or other high-risk ingredients, but adds that when replacement is not possible, soaking the sponge in water above 70 degrees Celsius for at least two minutes can significantly reduce bacterial contamination.

Using a sponge that dries quickly and can be washed in a dishwasher at a minimum of 60 degrees Celsius also helps. Earlier research found that dish brushes and microfiber cloths harbor fewer bacteria than sponges.