Five Second Rule
|Have you ever dropped food on the floor and wondered if it would be ok to eat it? Maybe one of your friends said "Five Second Rule!", referring to the idea that if you pick up the food within five seconds of dropping it on the ground, it would be free of germs, thus allowing you to eat it without fear. It's not clear from where this rule originated, but it is widespread in popular culture. There are conflicting views on whether or not this "rule" is valid. Some people (doctors included1) will eat food after dropping it on a surface no matter how many seconds have gone by; others are more stringent with the food they ingest and will not eat it even if it has merely brushed against a possibly contaminated surface.|
|The Five Second Rule prompted multiple studies by researchers and TV show hosts who wanted to put the myth to rest2-6. All of these studies tested a variety of foods dropped on a variety of surfaces coated with different bacteria, for varying times. They all found similar results - no matter how long the food was in contact with the surface, it would pick up bacteria. Let's explore the methodologies and results of these studies in more detail.|
|In the show MythBusters3, the hosts Jamie and Adam tested locations in their shop for the presence of bacteria using contact plates. They placed each plate on the floor for five seconds and noted the location. After incubating the plates for 24 hours, they counted the number of bacteria on each plate and found that there were different numbers of bacteria on each plate, even from locations immediately adjacent to each other. In order to eliminate the location of the surface as a variable, they coated surfaces with beef broth and then dropped pastrami (wet food example) or a cracker (dry food example) onto the surface for two or six seconds. They found that the pastrami picked up the most bacteria, but found no difference between the two- or six-second samples.|
|The study published in the Journal of Applied Microbiology5 performed similar experiments to see how many bacteria (Salmonella typhimurium, to be precise) would transfer from wood, tile, or carpet onto bologna or bread. They also went one step further to measure how long the bacteria could survive on dry surfaces. They found that >99% of bacterial cells transferred from tile to bologna after a five second exposure time. Further, they found that S. typhimurium bacteria could survive for up to four weeks on a dry surface. This is important because Salmonella is one of the most common food-borne pathogens associated with food poisoning and contamination of surfaces used to prepare food.|
|The most recent study of the Five Second Rule was published this month in the journal Applied and Environmental Microbiology6. The authors studied the effect of contact times on contamination of food from surfaces coated with the bacteria Enterobacter aerogenes, which is another common food-borne pathogen. They tested watermelon, bread with or without butter, and gummy candy on stainless steel, wood, tile, and carpet surfaces. Further, they tested contact time and the media with which they inoculated the surfaces with the bacteria. Each surface was inoculated with bacteria and allowed to dry for 5 hours, and then the foods were dropped onto each surface for <1, 5, 30, or 300 seconds. The authors found that the highest percentage of bacteria transferred onto watermelon, and that longer contact times do result in higher numbers of bacteria transferred onto the food. They also found that the nature of the food (wet versus dry) and the surfaces onto which the food was dropped had a significant effect on the numbers of bacteria transferred. Importantly, they disproved the Five Second Rule with their findings that some transfers take place in less than one second, or even instantaneously.|
|While these results may make you feel a little bit uneasy about eating food that has been dropped on the ground (or other surfaces), keep in mind that many surfaces are much "dirtier" than the kitchen counter or floor. How many of you wash your hands before eating? How about after handling money? A study of $1 bills7 found that 94% harbor bacteria, and 7% of those bacteria are pathogenic to healthy people. Most of us are guilty of being in a hurry and just scarfing down our food without thinking about the surfaces or hands with which it has come into contact, and most of the time we are ok after eating said food. Hopefully this blog hasn't changed any of your habits, but rather has given you food for thought (pun intended) about the Five Second Rule, and any other "rules" that you hear about in pop culture.
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