Monday, March 13, 2006

The 5-second Rule

Say you drop a chunk of chocolate chip from your cookie. How long does it take bacteria and germs to hop on it from the time it hits the floor?

In the absence of any scientific information, I used to go by the "5-second rule" that states you have 5 seconds to pick up the fallen crumb. After that, the creeps start to invade your wayward morsel. Knowing that the only functional purpose of my "rule" was to provide a sense of safety and propriety when I snatched back the broken piece of cookie, I recently set out on a search of the Internet to find the truth.

And the truth is, I cannot find any authoritative information on how long it takes for germs and bacteria to invade a target of opportunity. But I can't believe this hasn't been studied. There are all sorts of fascinating questions prompted by the issue: (1) Does the bit of food have to fall on top of the germs or can they move quickly and contaminate it. (2) If so, how fast and how far can germs move in response to a nutritious windfall? (3) Does this imply thinking or volition on the part of the germs or do they have some sort of autonomous sensor array dedicated to locating food? (4) Let's say germs do invade the morsel fairly quickly. In what numbers? (5) Does the risk increase with time?

This weekend, I observed the nearly instantaneous migration of water to a paper towel and wondered if this is a potential model for germ movement. But then I realized it was the absorption of the fibers in the towel that were "taking up" the water molecules. The paper towel was active, not the water. So there goes another theory.

I'd like some help with this. If anyone is reading this blog and has knowledge of this subject, please contact me.

The Stickler


Blogger Duncan said...

Mythbusters on Discovery Channel covered this one.

The Five Second Rule

Myth: if you pick up a piece of food that has fallen on the floor before five seconds is up, no bacteria will get on it
Test 1: MythBusters HQ samples

Jamie and Adam used contact plates to test various locations in the MythBusters shop for bacteria. Each contact plate was placed on the floor for five seconds and labelled with the location. They incubated the contact plates for 24 hours and then counted the number of bacteria on them.

They got different results from locations that were adjacent to each other, so they decided that it would be important to eliminate location as a variable in the test..
Mini-myth: Toilet seat is the cleanest spot in the house

While they were collecting samples around the shop, Adam also placed a contact plate on the toilet seat for comparison. It did have less bacteria colonies than the other samples, though it seems that the other samples were all collected from the floor.
Test 2: Evenly contaminated surface

In order to eliminate location as a variable they created some evenly contaminated surfaces with beef broth. They dropped wet food (pastrami) and dry food (cracker) onto the surface for two and six seconds. They also did a control sample for comparison.

The wet pastrami picked up more bacteria than the dry crackers, but there wasn't a discernable difference between the two-second and six-second samples. They would need to do more testing to single out time as a factor in the test.

Jamie: "I don't think the results were all that conclusive."
Mini-myth: Dog mouths are cleaner than human mouths

Adam and Lulu the Dog both licked a contact plate. After incubating the samples, the dog's sample had less bacteria colonies than Adam's.

Adam: "I don't eat my own poo"

According to LiveScience: "Despite a habit of licking things no human would dare, Fido's mouth is often touted as scientifically more sterile. Truth is, oral bacteria are so species-specific that one can't be considered cleaner than the other, just different."
Test 3: Contact plates on evenly contaminated surface

They decide to eliminate food as a variable in the test and instead just apply the contact plates to the beef brothed surface for two seconds and six seconds. Both showed tremendous amounts of bacteria with no real difference based on time.

They found that the amount of bacteria that was picked up depended on the moisture of food, the surface geometry of food, and the location that it was dropped on, but there was no correlation to the amount of time it was dropped.


10:10 PM  

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