That's right. Your beloved toilet-bowl licking, butt-sniffing companion is, "surprisingly," a possible source for tons of bacteria

"We can tell whether you own a dog based on the bacteria we find on your television screen or pillow case," said co-author Dr. Rob Dunn, a biology professor at North Carolina State University. Dunn and his colleagues led a citizen-run survey of the germs living on household surfaces,  which was published today in PLoS One.

To the dismay of hypochondriacs, humans are surrounded by germs. But don't fret! Most are harmless, and some are even beneficial.

"Microbiomes," or the variety of microbial species that inhabit any particular space, are the hot topic in science this year, as evidenced by Michael Pollan's extensive piece in last week's New York Times Magazine.

Major advances in the technology used to identify microbes have spawned a new age of microbiome research. Scientists are now trying define these tiny life-mates and where they live, as they can impact human health in unexpected ways.

Environmental biologists at North Carolina State University and the University of Colorado enlisted the help of citizen scientists to help determine what types of bacteria are found in houses. Forty homeowners used sterile Q-tips to collect biological samples from the surfaces of common objects and appliances found in the homestead.

Their nine survey locations included the kitchen cutting board, kitchen counter, refrigerator shelves, toilet seats, pillowcases, exterior doorknobs, television screens, and the seals of interior and exterior doorways.

 

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The nine sites sampled in each home. (Credit: Neil McCoy and Hayley Stansell)

Just over 7,726 phylotypes, or kinds, of bacteria were identified. Households with dogs had more types of bacteria, with greatest impact seen in the microbial diversity of TV screens and pillowcases.

Cats, the presence of children, carpet, and the use of garden pesticides did not influence which species were found.

"We wanted to know what variables influence the microbial ecosystems in our homes, and the biggest difference we've found so far is whether you own a dog," said Rob Dunn. "There are bacteria normally found in soil that are 700 times more common in dog-owning households than in those without dogs."

Given a dog's daily pursuits - running in fields, rolling in dirt, chasing cars - it isn't too shocking that it may ferry bacteria from outdoors to indoors. But it may have a positive impact on human health. A few studies have suggested that owning a dog while pregnant can reduce the likelihood of a child developing allergies.

Plus this isn't the first indication that dogs influence the household microbiomes. A report from earlier this year showed that parents tend to share more bacteria with family dogs than with their children.

The researchers were able to group household surfaces by the types of bacteria that resided on them. For example, doorknobs, pillow cases, and toilet seats hosted similar bacterial species, most of which came from humans.

We leave a microbial 'fingerprint' on everything we touch," said Dunn. "Sometimes those microbes come from our skin, sometimes they're oral bacteria and - as often as not - they're human fecal bacteria."

Microbes found on kitchen counters, cutting boards, and refrigerators formed another group, while TVs and doorways comprised a third category of similar bacteria.

The largest diversity of microbes was observed on TV screen and doorways, which may be due to less frequent cleaning of these surfaces.

Dunn and his colleagues are currently processing samples from another 40 homes and plan to conduct a national survey of 1,300 homes across the U.S.

"The larger sample size will help us better understand the range of variables that influence these microbial ecosystems," Dunn said. "Does it matter if you have kids or live in an apartment? We expect the microbial populations of homes in deserts to be different from the populations of homes in Manhattan, but no one knows if that's true. We want to find out."

 

Source: Dunn RR, Fierer N, Henley JB, Leff JW, Menninger HL. Home Life: Factors structuring the bacterial diversity found within and 2 between homes. PLoS One. 2013.