Can you quickly pick up a piece of food that has fallen on the floor and eat it calmly if less than five seconds have passed? The popular rule turned out to be a myth: bacteria may need less than a second to move from a contaminated surface to food. Moreover, they particularly quickly "attach" themselves to juicy products.
As reported by Science Blog, the conclusion is based on an experiment conducted by researchers at Rutgers University, Robin Miranda and Donald Schaffner, published back in 2016 in the journal Applied and Environmental Microbiology. The scientists conducted 2560 individual trials, testing how the transfer of bacteria is affected by the type of surface, the food item, and the duration of contact.
Dropped from a Height of 12.5 Centimeters
The experimenters used four surfaces: stainless steel, ceramic tile, maple laminate, and carpet.
They dropped four types of food: watermelon, white bread, buttered bread, and strawberry gummy candies.
The contact time also varied: less than one second, five seconds, 30 seconds, and five minutes.
Enterobacter aerogenes was used as the microorganism — a bacterium chosen by the researchers as a non-pathogenic model. The surfaces were deliberately contaminated and then left for about five hours. The food was dropped from a height of 12.5 centimeters.
After each trial, the food was placed in a sterile bag and examined. Of course, no one ate the experimental food.
Watermelon Turned Out to Be the Record Holder
The most vulnerable food item was watermelon. Under certain conditions, up to 97% of available bacteria transferred to it.
Moisture played a key role. As Schaffner explained, bacteria do not move on their own — liquid helps carry them. Therefore, the wet surface of the watermelon creates particularly favorable conditions for the almost instantaneous transfer of microorganisms.
The least bacteria were collected from the gummy candies in the experiment. Bread and buttered bread occupied an intermediate position, with results varying significantly from trial to trial.
Thus, not only the duration of contact is important. Humidity and the structure of the food itself are of great significance.
An Unexpected Result from the Carpet
Another interesting result concerned the surface. Under certain conditions, only about 0.2% of bacteria transferred from the carpet to the food, while tile and stainless steel could transfer much more.
The researchers explain this by the characteristics of carpet: the fibers hold onto bacteria, and due to the pile, the food only comes into contact with part of the surface.
This, of course, does not mean that food dropped on the carpet is safe to eat. It simply indicates that in the experimental conditions, the carpet transferred microorganisms worse than some hard surfaces.
Five Seconds Don’t Matter Here
Similar experiments have been conducted before. Back in 2003, student intern Jillian Clark at the University of Illinois contaminated laboratory tiles with E. coli and dropped cookies and gummy candies on them. Bacteria transferred to the food within five seconds. For this work, Clark later received a humorous Ig Nobel Prize in Public Health.
In 2007, researchers at Clemson University studied the transfer of salmonella from tile, wood, and carpet to bread and sausage. They also found that the duration of contact matters, but is far from the only factor.
But There’s No Need to Panic Over Every Fallen Piece
The authors of Science Blog point out an important limitation of the Rutgers University experiment. The surfaces were intentionally contaminated with a very large number of bacteria — about 10 million cells per 25 square centimeters. A typical dry home floor does not necessarily have such a bacterial load.
Therefore, the real risk primarily depends on where the food fell and what the surface was contaminated with. A dry floor in a home where no one is sick is one situation. A spot near a trash can or an area of the floor recently contaminated with raw meat juice is a completely different one.
The main conclusion of the experiment is simple: a five-second countdown does not make dropped food safe. Bacteria can transfer to it almost instantly, and moist foods like watermelon can collect especially high numbers of microorganisms.
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