Tales of the Kitchen Sponge

Posted in Food Safety,Salmonella on August 17, 2018

When I first moved in with my now husband, he had a dirty little habit that we had to compromise on.  I was raised on a dishcloth that was used for one day, then tossed in the laundry.  He was raised with a sponge.

We were a house divided.  He was a sponge guy, I was a dishcloth girl.  He had his reasons.  I had mine.  And to be honest, the thought of a sponge sitting around on the sink creeped me out. Whether it was because I always had a clean washing tool, or the fact that I am a scientist, I could only think about swirling bacteria around on my plate, drying it off, and eating on it again.

After trying out the sponge I found merit in it.  It was great at holding suds.  It was great at scrubbing.  I just couldn’t get past the creepy crawly microscopic grossness.  I looked for ways to use the sponge that I felt comfortable with.

As with any research, you find out things you want to now.  And thing that you really didn’t want to know.  Did you know that the kitchen hosts the largest microbiome in your entire home?  Even more so than your bathroom toilet!  All because of that innocent looking sponge!  In fact, they come in second to the highest bacterial load in your home, falling shortly behind drain traps.

If this creeps you out a bit, you are not alone.  German researchers found some interesting data on the not-so-innocent sponge.

What’s a Microbiome?

In a study on the microbiome found on used sponges, researchers identified the relative amounts and types of bacteria found on the household sponge.  Though it might sound ominous, a microbiome is not always a bad term.  There are all kinds of microbiomes.  The term microbiome is a generic term that describes a community of microorganisms that inhabit the environment and are composed of bacteria, fungi, and viruses.

Microbiomes can be healthy and keep pathogens in check, like the microbiome found on the skin.  There are also unhealthy microbiomes, like the ones that contain an unproportionate number of harmful bacteria and viruses.

The study analyzed both newly bought and unused sponges alongside 28 used sponges from private households.  As part of the study, households provided a brief history of the sponge usage and age as well as the cleaning activities (if any) performed on the sponge.

Ideal Environment for Germs

The household sponge is premier breeding turf for bacteria.  This goes for both harmless AND harmful bacteria.  This warm, moist environment consists of tiny crevices that allow plenty of space for bacteria to colonize and grow.

The microbiome on a sponge adapts based on what it comes in contact with.  What the sponge is used to clean, the skin of the person using it, and a variety of other factors affect the microscopic makeup of the sponge.  Common bacteria found on your kitchen sponge includes: Campylobacter ssp., Enterobacter cloacae, Escherichia coli, Klebsiella ssp., Poteus ssp., Salmonella ssp., and Staphylococcus ssp.  Bacterial densities of up to 5.4 X 10¹⁰ cells per cm² were found on most sponges.  That is 7 times the number of people inhabiting the earth!  In your tiny sponge!  Eek!

You’d think that the cleaning factor of soap would clean the sponge as well.  This was my husband’s logic as well as many others when I brought up the topic.  Unfortunately, that logic doesn’t hold up.  Those tiny crevices act as reservoirs of bacteria and disseminate those harmful microorganisms that lead to cross-contamination of food, hands, and surfaces.  Consider that the next time you wipe down your counter or sink with an old sponge.

Let’s Explore the Life of a Sponge

You know you are an adult when nothing makes you happier than opening up a new sponge.  That was actually a meme I came across during my research.  Clearly enough people feel the same way.

So, imagine this, you open up that plastic wrapper and pull out your virgin sponge.  You use it the first time.  Wet it thoroughly, add soap, scrub your dishes, rinse it out (maybe), and then it sits idly on the edge of your sink, slowly drying out.  It takes quite some time for a sponge to fully dry.  It is a sponge.  We use the term as a verb.  That’s how effective a sponge is at holding moisture.  During this time all the bacteria from the food, the dishes, the user’s hands, and anything else it has come in contact with is multiplying and multiplying.  Though it happens microscopically, you might notice some changes.  Most obviously, you might notice the smell.  That my friend, is a whole colony and microbiome building its family in its new home.

Another family meal is complete.  Now it’s time to do the dishes again.  You run the water, wet the sponge, add some soap, and start cleaning.  It’s not fun, but it’s necessary.  You smear the sponge all over the plate, the cutting board you used to cut up chicken, everything that has to be cleaned. You dry the dishes and put them away.  Did you wash your hands at any point?  Was this before or after you dried off the dishes.  Well that is a topic for another day.

Then you look at your worn sponge and think, “This sponge has seen some wear.  Can a sponge be cleaned?”  Perhaps you toss it in the dishwasher.  Maybe the microwave.  A “life hack” I saw somewhere said to boil it.  That sounds logical.  Sadly, none of these are smart options.

So, What Are My Options?

According to research, any cleaning methods often do more harm than good.  In fact, a bigger ratio of Chryseobacterium haminis and Moraxella osloensis were discovered in sponge samples that were reported as regularly sanitized.

Heating methods such as microwaving or boiling indicated a reduction in bacterial load of 60% in laboratory tests.  But this only happened the first time the sponge was cleaned.  Subsequent heating methods were not so successful.  The remaining 40% of bacteria that survived cleaning methods recolonized at a faster rate, effectively repopulating the sponge.

“Presumably, resistant bacteria survive the sanitation process and rapidly re-colonize the released niches until reaching similar abundance as before the treatment.”  Without competition, these bacteria had plenty of legroom to grow.

Should I Avoid the Sponge?

If I haven’t grossed you out yet, I don’t think I’ve done my job.  So, you might me thinking, “Should I avoid the sponge?”  You have options.  You might opt for the dish cloth that is sent to laundry.  Though if you are attached to your sponge, toss it regularly and skip the decontamination.

By: Heather Van Tassell, Contributing Writer (Non-Lawyer)