Wake Up and Smell the Dog Poo?

So many smells for a pooch to discover! Many of them, it seems, come directly from the rear ends of other dogs. Credit: RNuwer
                    
Thinking about Rust Belt cities like Detroit and Cleveland, fresh, clean air may not be the first association that comes to mind. But the urban atmosphere contains more than just human pollutants; it’s also home to teeming communities of airborne microbes. A new study reveals an icky addition to residents’ daily microbial doses in the Great Lakes cities: bacteria from dog feces, and lots of it.
         
Though microbes often constitute a major proportion of the organic aerosols in the atmosphere, the diversity and geographic dispersal of these unseen floating communities are poorly understood. Depending on the critter composition, inhaling this bacterial cocktail can result in health impacts, like allergic asthma and seasonal allergies. To fill the knowledge gap, scientists analyzed air samples from three populous Mid-Western cities—Chicago, Detroit, Cleveland—along with the small town of Mayeville, Wisconsin, that served as a control to contrast the urban centers. They used 100 air samples, taken both from the summer and winter months, to see if microbe presence changed according to sunshine or snow. Samples secured, the researchers identified the bacteria using the creatures’ DNA, comparing their results from a database of bacteria from known sources like leaf little, soil, and human, cow, and dog feces.
         
The scientists were shocked at the bacterial diversity they found. Their results, published in Applied and Environmental Microbiology (subscription required), contained between 200 to 300 types of organisms. A surprise twist, however, turned up in Cleveland and Detroit. “To our surprise, the airborne bacterial communities of Detroit and Cleveland most closely resembled those communities found in dog poop,” said lead author Robert Bowers, a graduate student in ecology and evolutionary biology at Colorado University, in a press release.
     
Especially in the winter, the two Midwestern cities had significant amounts of fecal bacteria in the atmosphere, most likely originating from dogs. Dog poo might have a greater influence on winter air composition, the researchers speculate, because bacteria-containing leaves have dropped and snow covers the ground, acting to sterilize potential microbial sources blow it. During summer, on the other hand, airborne bacteria can come from a more diverse array of sources, like soil, dust, leaves, and water bodies.
      
Lest East- and West-Coasters get too cocky about the cleanliness of their own air, the researchers also hope to test the atmospheric microbial communities of cities like New York and San Francisco. This way, they can see if bacteria display similar patterns in cities across the U.S. With information about the types of bacteria, where they come from, and what sort of seasonal variation they undergo in different locations, scientists can then investigate possible health impacts on humans.
     
Either way, dog owners should be all the more vigilant in picking up after their pooches. Based on the study, Chicago is apparently on top of their poop scooping, but Detroit and Cleveland should perhaps invest in some doggie bags.