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One of the most dangerous sources of virulent bacteria, including E. coli, Salmonella, Staphylococcus and others, is the typical kitchen sponge and 'dish cloths' in American homes. They provide a source of moisture, a ready food supply in the form of food particles, and an easy surface to which the bacteria may cling. They can easily be disinfected however, by placing in a microwave oven for 60 seconds. The odor is improved too!


Every kitchen has at some time or another been home to a sponge, that oh-so-versatile cleaning tool. It wipes up messes on countertops and absorbs liquid droplets quickly. Best of all, it's reusable.

However, that handy kitchen sponge can harbor more than moisture--things like foodborne pathogens, yeasts and molds. So Agricultural Research Service (ARS) scientists in Beltsville, Md., have tested several methods for reducing risks from harmful microbes hiding in reused sponges.

At the ARS Food Technology and Safety Laboratory in Beltsville, microbiologists Manan Sharma and Cheryl Mudd and two student interns did the testing. First, they soaked sponges at room temperature for 48 hours in a solution made from ground beef and lab growth medium to attain a high level of microbes (20 million per sponge) to simulate a very dirty sponge.

Then, they treated each sponge in one of five ways: soaked for three minutes in a 10 percent chlorine bleach solution, soaked in lemon juice or deionized water for one minute, heated in a microwave for one minute, placed in a dishwasher operating with a drying cycle--or left untreated.

The scientists chose these methods because they're commonly used in most household kitchens. They found that between 37 and 87 percent of bacteria were killed on sponges soaked in the 10 percent bleach solution, lemon juice or deionized water--and those left untreated. That still left enough bacteria to potentially cause disease.

Microwaving sponges killed 99.99999 percent of bacteria present on them, while dishwashing killed 99.9998 percent of bacteria.

As for yeasts and molds, the sponges treated in the microwave oven or dishwasher were found to harbor less than 1 percent (0.00001 percent). Between 6.7 and 63 percent of yeasts and molds survived on sponges soaked in bleach, lemon juice, deionized water or left untreated.

Thus microwave heating and dishwashing with a drying cycle proved to be the most effective methods for inactivating bacteria, yeasts and molds on sponges. These simple and convenient treatments can help ensure that contaminated sponges don't spread foodborne pathogens around household kitchens of today's busy families.

ARS is the principal scientific research agency of the U.S. Dep’t of Agriculture.




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