The skin is the human body's largest organ, colonized by a diverse milieu of microorganisms, most of which are harmless or even beneficial to their host. Colonization is driven by the ecology of the skin surface, which is highly variable depending on topographical location, endogenous host factors and exogenous environmental factors. The cutaneous innate and adaptive immune responses can modulate the skin microbiota, but the microbiota also functions in educating the immune system. The development of molecular methods to identify microorganisms has led to an emerging view of the resident skin bacteria as highly diverse and variable. An enhanced understanding of the skin microbiome is necessary to gain insight into microbial involvement in human skin disorders and to enable novel promicrobial and antimicrobial therapeutic approaches for their treatment.

The skin microbiome

Atopic dermatitis (AD) has long been associated with Staphylococcus aureus skin colonization or infection and is typically managed with regimens that include antimicrobial therapies. However, the role of microbial communities in the pathogenesis of AD is incompletely characterized. To assess the relationship between skin microbiota and disease progression, 16S ribosomal RNA bacterial gene sequencing was performed on DNA obtained directly from serial skin sampling of children with AD. The composition of bacterial communities was analyzed during AD disease states to identify characteristics associated with AD flares and improvement post-treatment. We found that microbial community structures at sites of disease predilection were dramatically different in AD patients compared with controls. Microbial diversity during AD flares was dependent on the presence or absence of recent AD treatments, with even intermittent treatment linked to greater bacterial diversity than no recent treatment. Treatment-associated changes in skin bacterial diversity suggest that AD treatments diversify skin bacteria preceding improvements in disease activity. In AD, the proportion of Staphylococcus sequences, particularly S. aureus, was greater during disease flares than at baseline or post-treatment, and correlated with worsened disease severity. Representation of the skin commensal S. epidermidis also significantly increased during flares. Increases in Streptococcus, Propionibacterium, and Corynebacterium species were observed following therapy. These findings reveal linkages between microbial communities and inflammatory diseases such as AD, and demonstrate that as compared with culture-based studies, higher resolution examination of microbiota associated with human disease provides novel insights into global shifts of bacteria relevant to disease progression and treatment.

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Temporal shifts in the skin microbiome associated with disease flares and treatment in children with atopic dermatitis

Functioning as the exterior interface of the human body with the environment, skin acts as a physical barrier to prevent the invasion of foreign pathogens while providing a home to the commensal microbiota. The harsh physical landscape of skin, particularly the desiccated, nutrient-poor, acidic environment, also contributes to the adversity that pathogens face when colonizing human skin. Despite this, the skin is colonized by a diverse microbiota. In this Review, we describe amplicon and shotgun metagenomic DNA sequencing studies that have been used to assess the taxonomic diversity of microorganisms that are associated with skin from the kingdom to the strain level. We discuss recent insights into skin microbial communities, including their composition in health and disease, the dynamics between species and interactions with the immune system, with a focus on Propionibacterium acnes, Staphylococcus epidermidis and Staphylococcus aureus.

/pdf/the-human-skin-microbiome-znvh6yxg29.pdf

The human skin microbiome

Atopic dermatitis (AD), one of the most common skin disorders seen in infants and children, usually has its onset during the first 6 months of life. The prevalence of AD is similar in the United States, Europe, and Japan and is increasing, similar to that of other atopic disorders, particularly asthma. AD has been classified into 3 sequential phases: infantile, childhood, and adult, each with characteristic physical findings. AD has a tremendously negative effect on the quality of life of patients as well as family, most commonly disturbing sleep. The condition also creates a great financial burden for both the family and society. The cutaneous manifestations of atopy often represent the beginning of the atopic march. On the basis of several longitudinal studies, approximately half of AD patients will develop asthma, particularly with severe AD, and two thirds will develop allergic rhinitis. Epicutaneous sensitization has been thought to be responsible, with subsequent migration of sensitized T cells into the nose and airways, causing upper and lower airway disease. Animal models and human observation concur with this theory. Preliminary prevention studies with oral antihistamines provide evidence that early intervention might slow the atopic march.

https://www.jacionline.org/article/S0091-6749(03)02370-4/pdf

Atopic dermatitis and the atopic march.

INTRODUCTION In the past 25 years, numerous topical and systemic drugs have been developed for the treatment of acne vulgaris The voluminous amount of clinical trial information has become increasingly difficult for individual physicians to monitor Clinical trials are a science no different than any other aspect of medicine There has been improvement in the design and performance of clinical trials in the past several years Currently, most authoritative opinions fully support the need for studies to be performed under the CONSORT and Cochrane principles We accept that many studies have not been as rigorously performed in the past as trials done in 2002 But to discard such studies is inappropriate, because they were done well according to the standards of the time Thus, for the time being, clinical opinion, based in part on formal discussion among expert colleagues with an interest in acne and a logical analysis of the literature, is not unreasonable as the basis for a Consensus Recommendation Such recommendations highlight the indications for use of medications and the optimal approach to the management of specific clinical problems Overall, the goal is to provide a comprehensive overview of rational therapy, which can form the basis for more uniform therapeutic strategies throughout the world, enhanced patient compliance, and more effective use of healthcare resources Several sets of guidelines have been developed for the treatment of acne during the past decade, including a practice guideline for the Oral Treatment of Acne in France (1999), Canadian Acne Treatment Guidelines (1995), German Guidelines for Acne Treatment (2001), Treatment of Acne Vulgaris: Guidelines for Primary Care Physicians (1991), and Guidelines of Care for Acne Vulgaris from the American Academy of Dermatology (1990) However, advances in medicine occur relatively rapidly, and practice guidelines may be out of date shortly after they are issued Thus, there is a continuing need to update existing recommendations so that recent advances in therapy can be brought to the attention of physicians in a timely manner In recognition of this need, this supplement to the Journal of the American Academy of Dermatology has been developed by a panel of physicians and researchers in the field of acne, working together as a Global Alliance to Improve Outcomes in Acne The mission of this group is to develop consensus recommendations for the treatment of acne, which are evidence-based when possible, and which include input from numerous countries The members of the group represent a broad list of international dermatologists with a special interest in acne and reflect a wide range of experiences and opinions The activities of the group have been coordinated by Dimensional Healthcare, Inc, and funded by an educational grant from Galderma As might be expected, some of the physicians involved in the development of this document have past or current, direct or indirect financial

https://www.jaad.org/article/S0190-9622(03)01563-9/pdf

Management of Acne: A Report From a Global Alliance to Improve Outcomes in Acne

SUMMARY

Quantitative aerobic cultures were obtained from fifty patients with chronic plaques, and from twenty with exudative lesions of atopic dermatitis. In the former, Staphylococcus aureus was isolated from 90% and the density exceeded 1 × 106/cm2 in 45% of the samples. In the exudative form, Staph. aureus was recovered in every case with a mean density of 14 × 106 organisms per cm2. Staph. aureus was the dominant organism not only in the lesions but in nearby clinically normal skin. Despite these high numbers, clinical signs of infection were lacking. Systemic and topical antibiotic therapy pro-duced a profound decrease in Staph. aureus density.



It is proposed that high numbers of Staph. aureus may aggravate the underlying lesion and be the source of Staph. aureus infections in contacts.

Staphylococcus aureus in the lesions of atopic dermatitis

Control of Free Fatty Acids in Human Surface Lipids by Corynebacterium Acnes

Quantitative Microbiology of the Scalp in Non-Dandruff, Dandruff, and Seborrheic Dermatitis

Sixty-one psoriatic patients were studied with regard to the quantities of Staphylococcus aureus on involved and uninvolved skin. About 50% of the patients carried S aureus , usually in low numbers. Staphylococcus aureus and resident cocci were more numerous on the lesions as compared to uninvolved skin. Occlusion with plastic film led to an explosive increase of S aureus in carriers, accompanied by aggravation of inflammation. Heavily colonized lesions responded less well to treatment. Because of increased exfoliation, psoriasis is an important source of hospital cross infection.

Richard R. Marples

Papers

Staphylococcus aureus in the lesions of atopic dermatitis

Control of Free Fatty Acids in Human Surface Lipids by Corynebacterium Acnes

Quantitative Microbiology of the Scalp in Non-Dandruff, Dandruff, and Seborrheic Dermatitis

Staphylococcus aureus in psoriasis.

A Method for Visualizing and Quantitating the Desquamating Portion of the Human Stratum Corneum