January 28, 2007 in Nation/World

Microwave: sponge’s best germ defense

Dennis O'brien Baltimore Sun
 

Germ-conscious consumers are snapping up a new generation of products designed to reduce the risk of catching a bug.

We’re not talking about antibacterial soaps, chlorine bleaches and ammonia-based cleansers. They’re old news. These days, you can minimize your health risks with antimicrobial pens and trash cans equipped with infrared sensors that trigger self-opening lids.

Still, one household product that spreads infection hasn’t changed much over the years: your kitchen sponge. But scientists say they’ve found a near-foolproof method for sanitizing even that old germ trap – make sure the sponge is wet, then nuke it in your microwave oven.

Why be so obsessive? Sponges are one of the key pathways for bacteria, viruses, parasites and other germs to spread in the home, causing many of the estimated 76 million cases of food-borne illnesses a year, hygiene experts say.

Some microbiologists recommend throwing sponges away after a week to keep the germs at bay. But almost nobody does.

“The kitchen sponge is a source of all sorts of microbes.” says Gabriel Bitton, an environmental microbiologist at the University of Florida.

Bitton and a team of university researchers say their recipe for making sponges less infectious is simple: microwave them on high for about two minutes.

“It won’t completely sterilize them, but it will knock out almost all of the bacteria,” Bitton said.

Specifically, the heat and drying process destroy bacteria and other pathogens that need water to survive, according to Bitton and other experts.

The results were the same for sponges and plastic scrubbing pads. The process works for “any standard cellulose sponge that can retain water, or a nonmetallic scrubbing pad, like those with nylon fibers,” Bitton said.

Don’t try this with metallic scrubbers unless you enjoy microwave fireworks, experts say.

In a study published in the Journal of Environmental Health, Bitton and other University of Florida researchers soaked up to 100 sponges and scrubbing pads in raw wastewater containing fecal bacteria, viruses, parasites and bacterial spores.

Then they microwaved the sponges for up to four minutes and wrung them out to determine the microbial load in the water.

Two minutes in the microwave killed 99 percent of all but the hardiest type of bacteria known to cause food poisoning – the Bacillus cereus spore.

Any microwave oven will work, but to keep the sponges and pads from burning up, they should be thoroughly soaked when placed in the microwave. And be careful when you remove the sponge – it will be hot, Bitton said.

The University of Florida released an advisory emphasizing the precautions last week after readers complained to news organizations that had failed to mention the measures in articles.

Microwaving is more effective than running sponges and cleaning pads through a dishwasher, experts say.

While a dishwasher helps, its water only reaches 140 degrees Fahrenheit. Tiny probes placed inside microwaved sponges and pads showed that they reached temperatures of up to 197 degrees, Bitton said.

Pathogens reach the kitchen by way of raw meats and vegetables from the grocery store, said Charles P. Gerba, an environmental microbiologist at the University of Arizona who was not involved in the study.

Most are washed down the sink, but some will cling to the sides of sinks and crevices in countertops and cutting boards – where even the most germ-fearing among us will unwittingly spread them when we use the ubiquitous sponge, he said.

Gerba, who has spent several years studying the cleaning practices and pathogen patterns found in the typical home and office, has uncovered some startling facts.

The average cutting board has 200 times more bacteria than a toilet seat, he said. And by the end of a week, a hand-size sponge can have more than a million bacteria, he said.

He recommends the frequent use of disinfectant cleanser on cutting boards and countertops, using paper towels instead of dishcloths for cleaning any kitchen surfaces and throwing out sponges after a week.

But if you want to keep the sponge beyond a week, “microwaving them isn’t a bad idea,” Gerba said.

Studies also have established that frequent laundering of dishcloths can rid them of up to 99 percent of the bacteria on them, said Dean Cliver, a professor of food safety at the University of California at Davis School of Veterinary Medicine

“It’s not so much a matter of killing as dilution. The detergent dislodges the bacteria and it will go down the drain,” Cliver said.

Cliver published a study in 1997 documenting similar results when he microwaved sponges. Cliver’s work is cited in Bitton’s report.

“We got it done in one minute, but if they want two minutes that’s fine. What’s a minute or two in the life of a bacteria?” Cliver said.

Bitton said that some people may be overly concerned about the microbial world. Not all microbes are harmful, and humans can’t live in a sterile environment. We need bacteria to digest our food, build up our immune systems and cleanse the soil.

“You’re never going to have a totally sterile environment in your kitchen. I don’t believe that,” Bitton said. “I’m a guy who says that kids should play in the yard, in the dirt. It’s the only way to build the immune system.”

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