|Example of canine Atopic Dermatitis, as seen|
in the manuscript we are discussing.
Atopic dermatitis (AD), which is also referred to as Eczema, is a very common dermatological disease, especially in children. It is estimated that AD affects 10% of children. The disease presents as dry, scaly, itchy skin. Atopic dermatitis can be especially problematic when the victim (often a child) itches the skin extensively, thereby increasing susceptibility to skin infections. Treatment of the disease ranges from controlling the itchy skin with soothing topical medication to bathing the patient in dilute bleach (the bleach bath technique).
In addition to genetics, there is evidence that AD has a microbial component. More specifically, research has linked the disease to Staphylococcus bacteria colonization that may play a role in flares and disease control. The bacteria and human genetics are thought to be linked in part by the impaired skin barrier function (e.g. control of water loss, acidity, etc) that results in an altered environment for the bacteria, and especially Staphylococcus, to grow.
What makes this week's study by Bradley et al particularly interesting over existing AD microbiome studies is that they investigate both the altered bacterial communities, as well as the altered barrier function of the diseased skin itself. Their study focused on canine AD, and so was conducted entirely in dogs. Canine AD affects approximately 10% of dogs, and perhaps more importantly, it closely resembles the human disease, thus providing information relevant to human medicine.
The group conducted their study with a cohort of 32 dogs, 15 of which were diagnosed with canine AD. Each dog had various skin sites swabbed for microbiome analysis by 16S rRNA gene sequencing (the standard approach for studying the microbiome). Sampling was done over time, so the temporal dynamics of the disease could also be visualized. Like previous studies, the group found that flaring skin was associated with an increased dominance of Staphylococcus in the microbiome (measured as relative abundance). They also found the diseased skin was associated with altered bacterial diversity, and that antimicrobial therapy restored the microbiome to a healthier state.
|Example of a non-invasive device used to measure skin|
The study really got cool when they evaluated the barrier function of the diseased skin and linked that data to their microbiome data. In the end, they found some links between microbiome diversity and some aspects of impaired barrier function. I emphasize some because the correlations were only between certain microbiome and barrier signatures. Overall this may suggest the AD microbiome signatures are the results of an altered skin environment due to impaired barrier function. Perhaps the presence of the bacteria are feeding into the progression of the skin flare? There are a lot of interesting research directions that this could go, and it will be exciting to watch where the group takes it next.
In the end, this is a cool study and it is worth reading. The group provides valuable insight into a common disease both for humans and dogs. Moving forward, I would be very interested in seeing the group look more into the links between skin barrier function and Staphylococcus colonization. This might include a heavier immunological study that further investigates the molecular response of the AD skin to the microbes. It will be interesting to see what they come up with.
So to totally wrap things up, I want to thank you for reading. This blog is not possible without you the reader. I would also love to hear from you about any questions, comments, or concerns. Feel free to leave a comment below, email me, or Tweet me.
Bradley, C., Morris, D., Rankin, S., Cain, C., Misic, A., Houser, T., Mauldin, E., & Grice, E. (2016). Longitudinal evaluation of the skin microbiome and association with microenvironment and treatment in canine atopic dermatitis Journal of Investigative Dermatology DOI: 10.1016/j.jid.2016.01.023