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The 5-second rule: Is it really safe to drop food on the floor and still eat it?

Posted 9:03 a.m. Thursday

Researchers at Rutgers University have bad news for anyone who's ever dropped a cookie on the floor and scooped it up, citing the "five-second rule" of food safety. There's no safe window of time to eat something dropped on the floor. Even without the benefit of legs, bacteria can get to it faster than you.

The five-second rule, long a maxim for children prone to dropping things, says that if something's been on the floor for five seconds or less, it's safe to eat. Rutgers researchers in New Brunswick, New Jersey, decided to test that.

According to Science Daily, they dropped four kinds of food (watermelon, gummy candy, bread, and bread and butter) on four different surfaces on which they'd deposited bacteria called enterobacter aerogenes, a cousin of salmonella. Then they analyzed the results.

The takeaway: Never eat watermelon dropped on a tile floor.

Watermelon was the most contaminated food, and the candy was the least, according to Donald Schaffner, a Rutgers professor and specialist in food science.

"Transfer of bacteria from surfaces to food appears to be affected most by moisture," Schaffner told Science Daily. "Bacteria don't have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer."

Additionally, food spilled on tile and stainless steel had more bacteria than food dropped on carpet. Rates of contamination varied on wood surfaces.

"The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food. Bacteria can contaminate instantaneously," Schaffner said.

But timing does matter in one way: The longer the food's on the floor, the more contaminated it is, and cross-contamination contributes to food-borne disease.

Although the veracity of the rule has been challenged on TV, Schaffner and his co-author, Robyn C. Miranda, said there has been little formal research on the topic. Their results were published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

Meanwhile, Harvard researchers have been filming bacteria to demonstrate how they can mutate and overcome antibiotics that are supposed to be lethal.

The videos have been wowing scientists ever since they were shown at an evolutionary biology conference last month, a report in The Atlantic says.

The scientists built a 2x4 foot petri dish and mounted a camera over it that took snapshots as the E. coli bacteria advanced.

"The researchers caution that their giant petri dish is not intended to perfectly mirror how bacteria adapt and thrive in the real world and in hospital settings, but it does mimic the real-world environments bacteria encounter more closely than traditional lab cultures can," wrote Ekaterina Pesheva in the Harvard Gazette.

That real-world environment includes your kitchen floor, so don't let your children pick up food there and eat it, lest they get an unwanted lesson in what E. coli, salmonella and other kinds of bad bacteria can do to the digestive tract.

EMAIL: jgraham@deseretnews.com

TWITTER: @grahamtoday

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