Sunday, October 9, 2011

Bacteria... in every breath you take

In case you needed a more compelling reason to scoop your dog’s poop than the general good deed of not leaving behind a present for someone’s shoe to discover, consider the fact that what you leave behind on the ground doesn’t always remain on the ground.

One person is likely to breathe in 860,000 bacteria every day1.  Where do these bacteria come from?  What kinds of bacteria are they?  Does where you live affect the kinds of bacteria that are likely to be floating around in the air- and in your lungs?

Scientists from Colorado strained the air for bacteria in Chicago, Cleveland, Detroit, and Mayville, WI over the course of six weeks in the summer and six weeks in the winter in order to answer exactly these kinds of questions.  In 5,000 cubic meters of air (that’s how much a person breathes in about a year and a half) there were 200-300 different kinds of bacteria from at least seven different bacterial phyla.  Side note: Living things that are in different phyla are generally distantly related to each other: for example seas urchins belong to the animal phylum that is most closely related to the animal phylum containing humans- we last shared a common ancestor 600 million years ago.

Even though bacteria in the air were very diverse, the kinds of bacteria found in different cities didn’t vary much.  In fact, there was a much greater change within one city from summer to winter than between two different cities.  In the summer there were generally more bacteria in the air than in the winter, especially in Detroit and Cleveland.  The researchers found that the main sources of airborne bacteria during the summer are likely to be the soil and the surfaces of leaves.  Since leaves aren’t out in the winter and the ground is frozen, this probably decreases the input of bacteria into the air.

So, where do the bacteria found in winter air come from? Dog feces, most likely.  In the winter, but not in the summer, a kind of bacteria called Fusobacteria are very abundant in the air.  These bacteria are commonly found in canine guts, but not in humans or livestock.  Want to avoid the bacteria of fecal origin? Plan your trips to Cleveland or Detroit for the summer.  But to be fair, the origins of aerial bacteria for other cities have yet to be discovered.

1Assuming a constant breathing rate of 12 times per minute, inspiring 0.5 liters each time, with a concentration of 100,000 bacteria per cubic meter of air.

Your can find this article at:

ResearchBlogging.orgBowers, R., Sullivan, A., Costello, E., Collett, J., Knight, R., & Fierer, N. (2011). Sources of Bacteria in Outdoor Air across Cities in the Midwestern United States Applied and Environmental Microbiology, 77 (18), 6350-6356 DOI: 10.1128/AEM.05498-11

1 comment:

  1. if smoker needs worning on every pack why dog keeping should not have worning?