Cleaning your kitchen sponge isn't preventing it festering with bacteria

When you first open a packet of kitchen sponges they start off so clean and innocent – so unaware of the bacteria magnets they’re about to become.

And while most of us are aware that they are dirty, dirty things – some even going to the trouble of ‘disinfecting’ them with boiling water or replacing them regularly – we’re still underestimating quite how filthy they are and the fact we can’t really do anything about it.

According to a new study from Scientific Reports, soaking your sponges in boiling water or microwaving them does nothing.

In fact, sponges that are treated in this way aren’t any cleaner than sponges left to fester on the side of your sink.

Though the researchers couldn’t detect any bacteria on newly-bought sponges, which you could say is a silver lining.

To get these results, scientists analysed 14 used domestic kitchen sponges taken from private homes in Germany.

They then separated each into two halves using sterile instruments before freezing them in order for them to conduct DNA extraction and ‘fluorescence in situ hybridization’ (FISH) staining.

The sponges’ owners were then asked if they regularly cleaned them (either by rinsing them in hot, soapy water or heating them in a microwave) and how often they changed them.

Which they tended to do monthly or weekly, by the way.

The FISH staining process let the researchers see how bacteria was distributed in the sponges and its density, as well as see how much of it there was in non-cleaned compared to cleaned sponges.

They found the sponges were packed with a class of bacteria called Gammaproteobacteria, which harbour pathogens that could lead to cholera and food poisoning.

Which the researchers noted was thanks to their, well, spongy nature – being full of “internal cavities” to hide in.

The researchers told Metro that kitchen sponges are the “biggest reservoirs of active bacteria in the whole house”:

“Kitchen sponges not only act as a reservoir of microorganisms, but also as disseminators over domestic surfaces,” they said, “which can lead to cross-contamination of hands and food, which is considered a main cause if food-borne disease outbreaks.”

And they confirmed that yes, cleaning them regularly doesn’t help.

“Regularly-sanitised sponges did not contain less bacteria than uncleaned ones,” they added.

“Moreover, ‘special cleaning’ even increased the relative abundance of both the Moraxella.

“Presumably, resistant bacteria survive the sanitation process and rapidly re-colonize the released niches until reaching a similar abundance as before the treatment.”

So if your sponge has been lingering in the sink for more than a week, perhaps it’s time to chuck it out and get a new one.

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