Don’t count on the ‘five-second rule,’ researchers say

five second rule

Photo: Mark Deibert/iStockphoto

New Brunswick, NJ – Forget about the so-called “five-second rule” regarding the safety of food that has been dropped on the floor. Researchers from Rutgers University have found that bacterial cross-contamination from surface to food can occur in less than one second.

“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food. Bacteria can contaminate instantaneously,” Donald Schaffner, a study author and professor and extension specialist in food science at the university, said in a press release.

Using the bacteria Enterobacter aerogenes, defined by researchers as “a nonpathogenic ‘cousin’ of Salmonella naturally occurring in the human digestive system,” researchers experimented with watermelon, bread, buttered bread and gummy candy on four different surfaces – stainless steel, ceramic tile, wood and carpet. Food remained on a surface for periods of less than one second, five seconds, 30 seconds and five minutes.

After recording nearly 2,600 scenarios, researchers determined that the watermelon was the food that became the most contaminated with bacteria, while gummy candy was contaminated the least. Bacteria on carpet moved less than bacteria on stainless steel and tile; transfer from wood was more variable.

Researchers concluded “the nature of the food and the surface it falls on” are equally or more important factors than the length of time the food is on the surface in determining how much bacteria transfer to food.

The study was published online Sept. 2 in the journal Applied and Environmental Microbiology.

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