Acne microbiome: From phyla to phylotypes.

Acne vulgaris is a chronic inflammatory skin disease with a complex pathogenesis. Traditionally, the primary pathophysiologic factors in acne have been thought to be: (1) altered sebum production, (2) inflammation, (3) excess keratinization and (4) colonization with the commensal Cutibacterium acnes. However, the role of C. acnes has been unclear, since virtually all adults have C. acnes on their skin yet not all develop acne. In recent years, understanding of the role of C. acnes has expanded. It is still acknowledged to have an important place in acne pathogenesis, but evidence suggests that an imbalance of individual C. acnes phylotypes and an alteration of the skin microbiome trigger acne. In addition, it is now believed that Staphylococcus epidermidis is also an actor in acne development. Together, C. acnes and S. epidermidis maintain and regulate homeostasis of the skin microbiota. Antibiotics, which have long been a staple of acne therapy, induce cutaneous dysbiosis. This finding, together with the long-standing public health edict to spare antibiotic use when possible, highlights the need for a change in acne management strategies. One fertile direction of study for new approaches involves dermocosmetic products that can support epidermal barrier function and have a positive effect on the skin microbiome.

What is new in adult acne for the last 2 years: focus on acne pathophysiology and treatments.

Acne affects more than 640 million people worldwide, including about 85% of adolescents. This inflammatory dermatosis affects the entire population, from teenagers to adults, which reinforces the need to investigate it. Furthermore, in adults, acne has serious consequences, including a psychological impact, low self-esteem, social isolation, and depression. Over the last years, the understanding of acne pathophysiology has improved, mainly thanks to the identification of the pivotal role of the microbiota. The aim of this review was to screen the most recent scientific literature on adult acne and the newly tested treatments. Clinically, therapeutic innovations for the treatment of acne have been recently developed, including pre/probiotics, new molecules, and innovative formulations associated, however, with fewer side effects. Moreover, clinical trials are underway to use off-label molecules that seem to be proving their value in the fight against adult acne.

Cutibacterium acnes and Staphylococcus epidermidis: the unmissable modulators of skin inflammatory response.

Acne is a multifactorial inflammatory dermatose that affects all age categories from teenagers to adults, resulting in important psychological impacts. Multiple hypotheses currently attempt to decrypt the physiopathology of this disease, and four main actors were identified as highly implicated in it: hyperkeratinization of the pilosebaceous follicle, hyperseborrheae, host factors (innate immunity) and skin microbiota. In this letter, we present results illustrating the impact of skin microbiota on inflammatory skin response, and how far the proper balance between each bacterial community, especially C. acnes and S. epidermidis, is crucial to maintain an appropriate inflammatory response on the skin. The data presented in this study demonstrate that within the skin microbiota, an imbalance between Cutibacterium acnes and Staphylococcus epidermidis, is able to induce the activation of inflammation-related markers such as IL-1ra, IL-6, IL-8, G-CSF and the molecules C5/C5a, soluble CD14 MIP-3beta, Serpin E1, VCAM-1 and beta-defensin-2. Moreover, S. epidermidis appears to have a more important role than C. acnes on the induction of inflammation-related markers, particularly on IL-6. This work is the basis of future in vitro studies to further understand acne physiopathology, inspiring the development of future innovative therapies based on skin microbiota modulation.

Atopic dermatitis: Role of the skin barrier, environment, microbiome, and therapeutic agents.

Atopic dermatitis (AD) is a chronic, inflammatory skin disorder characterized by eczematous and pruritic skin lesions. In recent decades, the prevalence of AD has increased worldwide, most notably in developing countries. The enormous progress in our understanding of the complex composition and functions of the epidermal barrier allows for a deeper appreciation of the active role that the skin barrier plays in the initiation and maintenance of skin inflammation. The epidermis forms a physical, chemical, immunological, neuro-sensory, and microbial barrier between the internal and external environment. Not only lesional, but also non-lesional areas of AD skin display many morphological, biochemical and functional differences compared with healthy skin. Supporting this notion, genetic defects affecting structural proteins of the skin barrier, including filaggrin, contribute to an increased risk of AD. There is evidence to suggest that natural environmental allergens and man-made pollutants are associated with an increased likelihood of developing AD. A compromised epidermal barrier predisposes the skin to increased permeability of these compounds. Numerous topical and systemic therapies for AD are currently available or in development; while anti-inflammatory therapy is central to the treatment of AD, some existing and novel therapies also appear to exert beneficial effects on skin barrier function. Further research on the skin barrier, particularly addressing epidermal differentiation and inflammation, lipid metabolism, and the role of bacterial communities for skin barrier function, will likely expand our understanding of the complex etiology of AD and lead to identification of novel targets and the development of new therapies.

The Skin Microbiome: A New Actor in Inflammatory Acne.

Our understanding of the role of Cutibacterium acnes in the pathophysiology of acne has recently undergone a paradigm shift: rather than C. acnes hyperproliferation, it is the loss of balance between the different C. acnes phylotypes, together with a dysbiosis of the skin microbiome, which results in acne development. The loss of diversity of C. acnes phylotypes acts as a trigger for innate immune system activation, leading to cutaneous inflammation. A predominance of C. acnes phylotype IA1 has been observed, with a more virulent profile in acne than in normal skin. Other bacteria, mainly Staphylococcus epidermis, are also implicated in acne. S. epidermidis and C. acnes interact and are critical for the regulation of skin homeostasis. Recent studies also showed that the gut microbiome is involved in acne, through interactions with the skin microbiome. As commonly used topical and systemic antibiotics induce cutaneous dysbiosis, our new understanding of acne pathophysiology has prompted a change in direction for acne treatment. In the future, the development of individualized acne therapies will allow targeting of the pathogenic strains, leaving the commensal strains intact. Such alternative treatments, involving modifications of the microbiome, will form the next generation of 'ecobiological' anti-inflammatory treatments.

Bacterial extracellular vesicles: A new way to decipher host-microbiota communications in inflammatory dermatoses.

Bacterial extracellular vesicles (EVs) are bilayered lipid membrane structures, bearing integral proteins and able to carry diverse cargo outside the cell to distant sites. In microorganisms, EVs carry several types of molecules: proteins, glycoproteins, mRNAs and small RNA species, as mammalian EVs do, but also carbohydrates. Studying EVs opens a whole new world of possibilities to better understand the interplay between host and bacteria crosstalks, although there are still many questions to be answered in the field, especially when it comes to microbiota-derived EVs. In this review, we propose to summarize and analyse the current literature about bacterial EVs and possible clinical applications, through answering three main questions: (a) What are bacterial EVs? (b) What are EV impacts on skin inflammatory disease physiopathology? (iii) What are the possible and expected clinical applications of EVs to treat inflammatory skin diseases?

Inflammatory skin is associated with changes in the skin microbiota composition on the back of severe acne patients.

Acne is the most common inflammatory skin disease, affecting up to 85% of the 11-30 years old world population. Skin microbiota appears as a key player involved in several skin dermatoses physiopathology. Here, we show that inflammatory skin is associated with changes in the skin microbiota composition on the back of severe acne patients but also on the face of patients where acne was scored as mild to moderate, comparing with healthy controls. Changes were observed particularly on skin commensals Propionibacteriaceae, Staphylococcaceae and Enterococcaceae families, suggesting the importance of the balance between skin commensals to maintain skin homeostasis and control skin inflammatory process.

Assessment of seven protocols to prepare Cutibacterium acnes bacterial lysates to measure its immunogenic potential and review of the literature.

Seven protocols were tested to prepare cell wall extracts from live Cutibacterium acnes. Different parameters were modified: thawing/freezing and sonication/freezing cycles, to impact on mechanical degradation of the bacteria. Finally, the immunogenic potential of the extracts generated was evaluated by measuring IL-8 releases using an in vitro skin explants system. The aim of this article was to compare the existing protocols from the scientific literature, and also propose a standardized method developed in our facilities.

Decrease in Diversity of Propionibacterium acnes Phylotypes in Patients with Severe Acne on the Back.

Propionibacterium acnes, a major member of normal skin microbiota, is subdivided into 6 phylotypes: IA1, IA2, IB, IC, II and III. This study investigated P. acnes subgroups on the face and back in patients with severe acne and in healthy controls. In 71.4% of patients with severe acne, P. acnes phylotypes were identical on the face and back, whereas this was the case in only 45.5% of healthy controls. The healthy group carried phylotypes IA1 (39.1%) and II (43.4%), whereas the acne group carried a high predominance of IA1 (84.4%), especially on the back (95.6%). In addition, the single-locus sequence typing (SLST) method revealed A1 to be the predominant type on the back of patients with acne, compared with a wide diversity in the healthy group. We report here that severity of acne on the back is associated with loss of diversity of P. acnes phylotype, with a major predominance of phylotype IA1. The change in balance of cutaneous P. acnes subgroups might be an inducing factor in the activation of P. acnes, which could trigger inflammation.