Sunday, November 8, 2009

Bacterial microbiomes on human skin

Nearly a year ago, I shared results of a study of the bacteria that live on human skin, including these fun facts:
  • Females have a higher diversity of bacteria on their hands than males . . . perhaps due to a slightly higher skin pH in women, or perhaps the mix of sebum, sweat, and lotions, or maybe even hormonal differences . . . they couldn't really say for sure at this point
  • Females have more bacteria living under the surface film of skin than males
  • 4, 742 different species of bacteria were found in the whole group of subjects
  • The species each of has on our hands is a rather unique mix--only 5 (out of 4,742) species were found on every hand in the group
  • Most of the 150 or so different species of bacteria found on skin of an individual hand are beneficial or harmless . . . only a small minority are pathogenic
  • The diversity of bacteria differs between a person's right hand and left hand
  • Hand washing (as practiced in this group) did not remove many of the bacteria (or the populations recovered rapidly after washing)
Recently, another study was published that gives us an even more complete picture of the micro-ecology of human skin.  The report, published online a few days ago by the journal Science, provides an inventory of what organisms live where on the human skin.

A few fun facts about the bacteria, viruses, and fungi of the human skin gleaned from the new study:
  • Microbes on the skin outnumber human cells by at least 10 times (about 100 trillion microbial symbionts)

  • Microbial community composition is determined primarily by habitat (well, of course!)

  • The composition of microbial communities varies widely from one person to another

  • The compostion of microbial communities for an individual human do not vary much over time

  • Some locations of the skin harbor more diverse communities than even the mouth or gut
Want to know more?
Bacterial Community Variation in Human Body Habitats Across Space and Time.
Elizabeth K. Costello, et al. 
Science Express, 5 November 2009, online .
doi: 10.1126/science.1177486
[Recent study on human flora]

Bacteria Flourish in Favorite Ecosystems on the Human Body
Laura Sanders
Science News November 5, 2009
[Nice summary of the study's importance and implications]

Variation In Bacterial Populations From Person To Person Surprises Researchers

C. Paddock
Medical News Today 6 November 2009
[Press release about the new study]

Skin Ecology
K. Patton
The A&P Professor 18 November 2008
[My previous article on the topic.  Includes links to other articles.]

Why cells cooperate

Here's a nice little "animated clay" video that zeroes in on the "society of cells" concept that lies at the heart of homeostasis.   Because it goes on to emphasize the role of reproductive cells in a multicellular organism, it may be useful to help our A&P students connect reproduction to the concept of overall body homeostasis.

I saw this video on public radio's Science Friday website, where they have a weekly video recommendation.

The video comes from a collection of videos at that are truly amazing.  Not very many directly relate to human anatomy and physiology . . . but, wow, they are fascinating.  For example, a recent posting discusses how mitochondria and other erstwhile endosymbionts can play a variety of roles such as acting as lenses for simple animals. I teach the serial endosymbiosis theory (SET)  in my A&P course . . . so this little factoid may help spice up that discussion.

So watch the FREE video about cell cooperation in a multicellular organism and let me know what you think!

H1N1 teaching moments

Although the typical A&P class is not focused primarily on pathology, we certainly do use pathology frequently as a tool to illustrate "normal" structure and function by looking at what goes wrong in injury and disease.  This works especially well when a disease or injury . . . or affected celebrity . . . is in the current news.  The current pandemic H1N1 outbreak gives us opportunities to teach some important concepts:
  • what do "public health" scientists do, and how do they do it?
  • what is a virus and how does it affect cell and body function?
  • how do vaccines protect the body?
  • why do some infections have a greater affect on some people than others?
  • how are viral infections spread?  how are they treated?
A recent news release posted at Science Daily summarizes a striking issue related to the flu vaccinations.  It highlights a paper recently published in The Lancet, which concludes that vaccination campaigns can be underminded by the public's tendency to link coincidental health events with vaccination campaigns.

Haven't we all see and heard of such associations?  They are even promoted by some otherwise trustworthy media outlets.  For example, many people are convinced of the strong relationship between certain vaccine preservatives and autism . . . even though thorough scientific investigation has shown no link.  An "outbreak" of Guillain–BarrĂ© Syndrome during the 1976-77 swine flu vaccination program turns out to be consistent with the number of people expected to contract this syndrome whether or not a vaccination program occurred.

In short, people get sick all the time and we should not automatically conclude that coincidental events are necessarily cause-and-effect scenarios . . . or even related at all.  And yet . . . we do.

This information is useful in teaching about how the scientific method can be used to answer questions.  In addition, the CDC's current surveillance methodology can be explored to illustrate how a scientific approach can be used in practical ways to watch for actual problems that could arise in a vaccination program.

In a somewhat related development, psychologists recently reported in Psychological Science that seeing and hearing a person sneeze can trigger fear or a "doom-and-gloom" attitude in healthy individuals.  I guess we should be cautious when exposed to sneezes, but the study showed that we tend to take such stimuli far more seriously than we realized.

Want to know more?
Pandemic Flu Vaccine Campaigns May Be Undermined By Coincidental Medical Events.
Cincinnati Children's Hospital Medical Center ScienceDaily. (2009, November 6)
[News release summarizing conclusions of a scientific study]

Importance of background rates of disease in assessment of vaccine safety during mass immunisation with pandemic H1N1 influenza vaccines
Black, S. et al.
The Lancet (early online publication) 31 October 2009
[Original peer-reviewed article]
Sneezes Provoke Fears Beyond Illness
Karen Hopkin
Sceintific American Online November 4, 2009
[Link to the podcast version or read the text summary]
[Here's an interesting clip to add to your PowerPoint or course web page . . . the first filmed sneeze ever recorded!  It was made with Thomas Edison's kinetoscope and was the first motion picture copyrighted in the United States.  Click here to see it ]