Good Germs

November 6, 2015

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I’m looking out my window at a gorgeous fall day, the kind of day that makes you notice the variety of trees and plants in their different stages of seasonal metamorphosis.  The kind of day that makes you wish you were outside, where things are fresh and alive, instead of in the hermetically sealed sterility of the great indoors.

Except it’s not sterile.  The indoor environment, where the vast majority of modern humans spend the vast majority of their time, is in many ways as lush as the woods on the Milwaukee County Grounds on which I am gazing.  Researchers are beginning to catalog the richness of the indoor microenvironment – the bacteria, fungi, and other microorganisms living on all the surfaces of our homes, schools, offices, hospitals, etc. – with an eye toward understanding how it affects us and vice versa.  Among the findings coming from The Wild Life of Our Homes:

  • The average person sheds about 37 million bacteria per minute into the interior environment; homes and even rooms (including hospital rooms) develop unique microbial identities from their inhabitants
  • Over 40,000 species of fungi have been identified inside homes – this is more than the total number of named fungal species in North America
  • The composition of the indoor microbial community can affect the risk of allergic and immune diseases such as asthma, inflammatory bowel disease, and diabetes
  • The presence of pets alters the indoor microbiome, in ways that may be healthier for the human inhabitants

There has been a huge advance in the past decade of our understanding of the human microbiome.  Health and disease rely in large part on the complex interplay between our genes, the micro-organisms inhabiting our skin and respiratory and GI tracts, and other environmental factors such as diet, exercise, and air- and water-borne contaminants.  The implications range from understanding how antibiotic resistance can spread through a community due to antibiotics use in concentrated animal feeding operations, also known as CAFOs or “factory farms” (farm workers become colonized with resistant bacteria and spread them for days); to the use of fecal transplants for treatment of a variety of conditions including C.difficile colitis.  But now we are also developing a better comprehension of how our immediate surroundings influence the microbial world within our bodies.

It starts early in life.  Babies born by Caesarean section develop a different intestinal microbiome, one in which skin flora predominates, than those born vaginally, and these differences can last for years.  This appears to explain some of the findings of a variety of diseases that are more common among babies born via C-section.  Some of the relationships, though, are more complicated than believed.  For example, scientists had hypothesized that homes in rural environments had richer microbial profiles than those in urban areas, which would go along with the observed lower rates of allergic diseases in rural areas (supporting the hygiene hypothesis, which posits that early exposure to microbes elicits healthy immune responses and protects against such diseases).  However, maps from the Wild Life of Our Homes project show such a relationship between rural setting and microbial diversity for fungi, but an opposite one for bacteria.  Also, a study showed that buildings, including hospitals, with recirculating air systems have less microbial diversity, and more pathogens, than those with more exposure to outside air.  As I said, it’s complicated.

So why do I bring this up?  In part because I think it’s really cool.  But also to raise awareness that microbes are necessary and usually good, and require appropriate care.  We can support efforts to reduce unnecessary antibiotic use in the food chain and in clinical care Avoid overuse of antibacterial soaps and sanitizers, which are no better than conventional cleaners and disrupt bacterial ecology of a community when they enter the water supply.  Open the windows.  Get a dog.


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