Atopic dermatitis
Atopic dermatitis (AD) is associated with dysbiosis of cutaneous microbiota and diminished diversity in microbial communities.6,7 There is also a robust epidemiologic relationship between the cutaneous and gut microbiomes and AD.8 Many studies have looked at the role of the microbiome in AD, including the role of Staphylococcus aureus, because it selectively colonizes the lesional skin of AD patients but is notably lacking on the skin of most healthy people.
In a 2017 literature review, Bjerre et al. found that while the data were not extensive, AD-affected skin was characterized by low bacterial diversity with S. aureus and Staphylococcus epidermidis more abundant. Also that year, Williams and Gallo reported on a prospective clinical trial in children that colonization by S. aureus occurred before the emergence of AD symptoms.9 In 2018, Clausen et al. reported on an observational case-control study of 45 adult healthy controls and 56 adult patients with AD between January and June 2015 to evaluate skin and nasal microbiome diversity and composition and to elucidate the relationship between disease severity and filaggrin gene mutations in AD patients. Next-generation sequencing targeting 16S ribosomal RNA was used to show that microbiome diversity was lower in the lesional skin, nonlesional skin, and nose in AD patients compared with controls. Such diversity was also found to be inversely correlated with disease severity, and microbiome composition in nonlesional AD skin was found to be associated with filaggrin gene mutations. The authors concluded that host genetics and skin microbiome may be connected in AD.10
However, the role of S. aureus in AD and the effect of its presence on microbiome diversity is still unclear. Marrs and Flohr note that the eradication of S. aureus does not appear to account for improvement in AD and increase in bacterial diversity after the use of antimicrobial and anti-inflammatory therapy.11
Rosacea
Rosacea is a chronic inflammatory skin condition long associated with Demodex mites (Demodex folliculorum and Demodex brevis).12 In rosacea-affected skin, Demodex mites are found to occur in greater density than in unaffected skin.13 Other microbiota-linked alterations have been detected on the skin and in the small intestines in cases of rosacea.14 One twin study showed that increased levels of Gordonia correlated with rosacea severity.15 A study in Korean women with rosacea demonstrated a reduction of Peptococcaceae, Methanobrevibacter, Slackia, Coprobacillus, Citrobacter (genus), and Desulfovibrio and an increased amount of Acidaminococcus, Megasphaera, and Lactobacillales in women with rosacea.16
Other studies have shown that treating bacterial overgrowth in the gut can improve rosacea.17 In my favorite recent study,18 complement appeared to affect microbial diversity and richness of the skin and the gut in mice, demonstrating that the immune system plays an important role in rosacea and the skin and gut microbiome. Certainly we have a lot to learn before we can make specific recommendations, but I feel certain that this area of research will unlock some of the mysteries of rosacea. To read more about what to tell your patients about the microbiome and rosacea visit the blog at STSfranchise.com.