Researchers Put the ‘Five-Second Rule’ to the Scientific Test

New scientific research has found that the amount of time a piece of food spends on the floor does in fact influence bacterial transfer, but food contamination can occur instantaneously, proving that the popular ‘five second rule’ is an oversimplification.

Researchers from Rutgers University put the legend of the ‘five second rule’ to the test by testing four different foods (watermelon, bread, bread and butter, and gummy candy) on four different household surfaces (stainless steel, ceramic tile, wood and carpet), for four different periods of time (less than one second, five, 30, and 300 seconds).

Enterobacter aerogenes, a nonpathogenic ‘cousin’ of Salmonella was used as the bacteria type. Each contact surface spot was inoculated with 1mL of enterobacter aerogenes using eight to ten drops spread over 5x5cm of surface. The surfaces dried completely before the foods were dropped. A total of 128 scenarios were replicated 20 times each, yielding 2,560 measurements. Post-transfer surface and foods were analyzed for contamination.

The results showed that contact time does influence bacteria transfer, with more bacteria transferred at longer contact surface times. The transfer of bacteria from surfaces to food appeared to be most affected by the moisture of the food as shown by transfer of E. aerogenesfrom tile, stainless steel, wood and carpet to watermelon, which had the most contamination. The gummy candy had the lowest levels of contamination.

The topography of the surface was significant in the transfer of bacteria. Carpet had the lowest transfer rates, with the other surfaces comparable, although the contamination of gummy candy rose substantially at the 300 second mark compared to the other surfaces.

In a sense, the authors concluded that the five-second rule is “real”; that longer contact time results in more bacterial transfer, however transference can occur instantaneously. The research also shows other factors, including the type of food and surface it falls on, are of equal or greater importance.

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