The Role of the Skin Microbiota in Acne Pathophysiology

S. Ramasamy; E. Barnard; T.L. Dawson Jr; H. Li

Disclosures

The British Journal of Dermatology. 2019;181(4):691-699. 

In This Article

Summary and Conclusions

The role of the skin microbiota in acne pathogenesis and progression has been investigated for decades, but still remains to be fully elucidated. Initially, culture-based investigations were hampered by biases based on the ability to grow multiple relevant microbes quantitatively. Even now, with less biased sequencing-based methods, sampling, homogeneous lysis, and choice of analytical methods remain challenging issues. Throughout this review we have utilized the recently proposed nomenclature change of Propionibacterium to Cutibacterium. We understand the confusion surrounding this historic organism, but in an effort to remain consistent we have chosen to use Cutibacterium throughout.

The sebaceous skin sites where acne occurs are dominated by Cutibacterium as prokaryotes and by Malassezia as eukaryotes, both of which can at different times and under different circumstances function as commensal or pathogen, depending on multiple factors in strain populations and host status (Figure 1). To date, quantitation of Cutibacterium in affected and unaffected skin remains controversial, but most literature and current opinion supports a numerical increase in acne lesions. It also remains to be determined whether there are numerical differences in the fungal (Malassezia) component. It is possible that longitudinal studies of individuals during treatment with either specific antimicrobials (antifungal vs. antibacterial) or the sebum secretion blocker isotretinoin may clarify the role of each kingdom.[81] It is plausible that acne pathogenesis involves changes in the distribution of specific strains and that the altered microbial community is influenced by host physiology (Figure 2). Furthermore, it has been shown that interactions between C. acnes and other bacteria, for example S. epidermis, are important for skin health.[24,82,83]

Further understanding of changes in the physiology of the various bacterial species and strains, beyond density and diversity, will be required to define both their exact role and, hence, potential intervention points in acne pathogenesis and treatment.[34] It will also be necessary to define the presence/absence, physiology and involvement of any fungal species, which may or may not play a significant role. With further investigations using robust, modern analytic tools in longitudinal studies with a large number of participants, it may be possible to determine whether microbiota plays a causal role, is primarily involved in exacerbation of acne, or is merely a bystander. Taking into consideration all currently available data and the known complexity of microbe–microbe and microbe–host interaction, it seems that the most parsimonious outcome is that acne is the result of a complex interplay between the microbiome and the host, and not the singular effect of any specific microbe or event.

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