Sharing is not always caring: the truth behind double dipping

Emily Beckett
23 January 2012

We’ve all seen this situation at some sort of gathering with family or friends; someone takes a pre-bitten chip and puts it back into the shared bowl of dip.

While reactions to this habit vary from indifference to disgust, researchers have concluded that double dipping is actually quite gross.

We all have hundreds of types of bacteria in our mouths. Many of these are harmless, but there are some types that we should worry about spreading, such as Streptococcus, Staphylococcus and Neisseria. Bacteria are not alone in causing disease: viruses are also known to be spread through saliva or saliva droplets. The flu, SARS and mono can all be spread by contact with the saliva of an infected person.

Did You Know?
One type of the Neisseria bacteria, Neisseria meningiditis, is one of the major causes of bacterial meningitis.

That’s why Dr. Paul Dawson at Clemson University, with the help of some students, decided to take the question of double dipping to the lab. They measured how much bacteria ends up in different types of dips after biting into a cracker and putting it back into the dip. Although the amount of bacteria passed on from the cracker depended on the thickness and acidity of the dip, the average amount was about 12,000 bacteria for every milliliter of dip.

Did You Know?
Exposure to as few as 1,000 bacteria could be all that's needed for Streptococcus pyogenes to cause infection. This bacteria causes strep throat, skin infections and, very rarely, flesh-eating disease.

But there is some good news after all: because dips have lots of ingredients, some of these might have natural antimicrobial properties that prevent the bacteria from growing. But we shouldn’t rely on the ingredients to keep us from getting sick, since bacteria can be good at adapting to new environments.

Did You Know?
Freshly crushed garlic contains allicin, which has a variety of antimicrobial activities.

It is also important to remember that just because you don’t feel sick, doesn’t mean that you are not carrying a contagious bacteria or virus. It can take up to four to seven days to feel the symptoms of meningitis. So, while you think you aren’t spreading any bug because you feel perfectly healthy, you're only a day or two from being sick yourself and sharing it with everyone around you.

Next time you are having a snack of chips and dip with some friends, make sure it’s only food that you’re sharing and don’t double dip.

References:

Ankri S and Mirelman D (1999) Antimicrobial properties of allicin from garlic. Microbes Infect. 1:125-9

Schmid-Hempel P and Frank S (2007) Pathogenesis, disease and infectious dose. PLoS Pathogens. 3: 1372-1372

Trevino J et al. (2009) Effect of biting before dipping (double-dipping) chips on the bacterial population of the dipping solution. Journal of Food Safety. 29: 37-48

Zaura E et al. (2009) Defining the healthy “core microbiome” of oral microbial communities. BMC Microbiology. 9: 259-271

Learn More!

CDC information about meningitis

CDC information about mononucleosis

CDC information about strep

Article first published on June 14, 2010.

Published in Health

Emily Beckett

I received my undergraduate degree in Biopharmaceutical Sciences at the University of Ottawa. I am currently a master's student at the University of Toronto. My lab is interested in several bacterial pathogens: Salmonella, E. coli and S. aureus. My research focuses on viruses that infect S. aureus that could be used as an alternative to antibiotics. The enemy of my enemy is my friend!


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