Your Pooch Could Raise Your Home's Bacteria Count

Study found more germs and a wider variety of bacterial types in houses with dogs

By Mary Elizabeth Dallas

HealthDay Reporter

WEDNESDAY, May 22 (HealthDay News) -- Man's best friend may bring millions more microscopic pals into the average human home, a new study suggests.

Researchers from North Carolina State University and the University of Colorado found that homes with dogs have more bacteria than other homes, including germs rarely found in households without dogs.

"We can tell whether you own a dog based on the bacteria we find on your television screen or pillowcase," study co-author Rob Dunn, associate professor of biology at NC State, said in a university news release.

The researchers involved 40 homes. Dunn and his colleagues wiped nine of the common surfaces in these residences -- TV screens, kitchen counters, toilet seats, refrigerators, pillowcases and door handles -- with sterile swabs to determine the types and amount of bacteria present.

The researchers found more than 7,700 types of bacteria in the homes, with unique groupings of bacteria depending on the location tested. For instance, bacteria found in refrigerators, on kitchen counters and on cutting boards were usually similar since they all related to food. The bacteria on doorknobs, pillowcases and toilet seats were also similar, but came more often from humans.

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

But what about differences between houses? "The biggest difference we've found so far is whether you own a dog," Dunn said. "For example, there are bacteria normally found in soil that are 700 times more common in dog-owning households than in those without dogs."

The study showed bacteria in homes can be grouped into three "habitats" or categories: places people touch, places touched by food and places that collect dust. The researchers pointed out the bacteria found on pillowcases in two different homes is likely more similar than bacteria found in the same home but in another "habitat."

"This makes sense," Dunn added. "Humans have been living in houses for thousands of years, which is sufficient time for organisms to adapt to living in particular parts of houses. We know, for example, that there is a species that only lives in hot-water heaters. We deposit these bacterial hitchhikers in different ways in different places, and they thrive or fail depending on their adaptations."

The study was published May 22 in the journal PLOS ONE. The researchers plan to conduct a larger study involving another 40 homes as well as samples from a national survey of 1,300 homes across the country.

"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."

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