Household dust is full of living organisms that are determined, in large part, by where the home is located and who is living in it, finds a new study that includes some surprising revelations.
Homes with a greater ratio of male occupants, for example, were found to contain large amounts of skin and fecal-associated bacteria, while women-dominated households contained an abundance of vaginally shed bacteria that somehow wound up in dust.
The study, published in the latest issue of the Proceedings of the Royal Society B, is believed to be the most extensive ever on microorganisms found in household dust.
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Senior author Noah Fierer told Discovery News that there are "millions of bacteria and fungi living inside our homes."
Fierer is an associate professor of Ecology & Evolutionary Biology and a fellow in the Cooperative Institute for Research in Environmental Sciences at the University of Colorado.
He and his colleagues used DNA sequencing and high tech imaging to analyze dust samples from approximately 1,200 homes across the United States. They used volunteers to help collect the material.
They discovered that indoor fungi mostly originates outside of the home, such that the geographical location of any home strongly predicts the types of fungi existing within dust.
"If you want to change the types of fungi you are exposed to in your home, then it is best to move to a different home, preferably one far away," Fierer and his team said.
Bacteria, on the other hand, were largely predicted by the home's possible inhabitants, including humans, pets and even insects.
Fierer said, "Our bodies are clearly the source for many bacteria that end up in our homes."
The researchers suspect that body size, relative abundance, and hygiene practices are why men tend to shed more Corynebacterium and Dermabacter (the skin-associated species), as well as the poop-associated Roseburia.
The vaginal-linked bacteria Lactobacillus, discovered in homes with a larger ratio of women, provides evidence that clothes do not fully contain the spread of microorganisms produced by our bodies. Members of this genus are actually thought to protect against allergies and asthma, based on earlier research, but further studies are needed to confirm how this, and other bacteria found in dust, impact human health.
Dogs and cats had such a dramatic effect on dust bacterial communities that the researchers could predict, with around 92 percent accuracy, whether or not such animals were in the home, just based on bacteria alone.
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While some people clearly suffer from allergies related to dander and other materials released by pets, Fierer said future research is needed to better clarify the health implications of animal ownership. So far, the news is good for dog lovers, as he pointed out that "previous work conducted by other groups has shown that living with a dog at a young age can actually reduce allergies."
Jonathan Eisen of the University of California at Davis and the Department of Education Joint Genome Institute has been working on microbial diversity studies for over two decades.
Eisen said the new work "is truly groundbreaking in many ways," due to its scope and the way that it engaged the public (he was one of the dust-collecting volunteers). He explained that such research is important because dust could be used to monitor environmental and other changes, and it could even serve as "a reservoir for genes involved in resistance to antibiotics, and much more."
Rachel Adams, a scientist specializing in plant and microbial biology at the University of California at Berkeley, said, "Recent studies are showing that the buildings where we spend most of our time contain great assemblages of microorganisms that you cannot see, and for the most part, those ‘cohabitants' of our homes are just along for the ride, neither harmful or offering much benefit."