Skin Microbiome Handbook

From Basic Research to Product Development

Nava Dayan, Nava Dayan

• Publisher: Wiley-Scrivener
• Year: 2020
• ISBN:
  9781119593027
• Edition: 1
• Topic: Médecine
• Subtopic: Dermatologie

The book provides a comprehensive detailed summary of current status on skin microbiome research in health and disease as well as key regulatory and legal aspects.

In the past decade, interest and technology have greatly advanced to unravel the nature and effect of skin microbiome on our health. Diseases such as atopic dermatitis and acne are at the forefront of this research, but also other conditions such as skin cancer are under investigation. In addition, mapping of the skin microbiome has gone from basic to more detailed with attempts to correlate it to various ages, ethnicities and genders. In parallel to mapping it, a great deal of research is dedicated to understanding its functionality and communication (and hence effect) on human cells.

The Skin Microbiome Handbook is a summary of current status of knowledge, research tools and approaches in skin microbiome, in health and disease. It contains the following categories: healthy skin microbiome and oral-skin interaction; skin microbiome observational research; skin microbiome in disequilibrium and disease; skin's innate immunity; testing and study design; regulatory and legal aspects for skin microbiome related products. The 18 chapters of the book are written by carefully selected leaders in the academia and industry exhibiting extensive experience and understanding in the areas of interest.

Part 1
HEALTHY SKIN MICROBIOME AND ORAL-SKIN INTERACTIONS

1
The Microbiome of Healthy Skin

Samantha Samaras¹* and Michael Hoptroff^2†

¹ Beauty & Personal Care Science and Technology, Unilever, United States

² Beauty & Personal Care Science and Technology, Unilever UK Limited, UK

Abstract

Over the last decade, radical advances in sequencing technologies have provided the tools with which to characterize microbial communities with unprecedented completeness and the consequent adoption of the term microbiome to describe the totality of microorganisms associated with a particular ecological niche. The application of these techniques has driven a renaissance in microbiology and nowhere is this truer than in our rapidly advancing understanding of the human-associated microbiome in all its complexity.

The work of the Human Microbiome Project and numerous other research groups has led to characterization of the skin microbiome in healthy and pathological skin, across body sites and populations. The emerging picture is one of a holistic association between skin and microbiome where healthy skin is the foundation of a balanced microbiome and where a balanced microbiome contributes to maintenance of healthy skin.

Keywords: Antimicrobial lipid, antimicrobial peptide, commensal microbe, microbiome, pathogen

1.1 Introduction

1.1.1 Retrospective

From the 1950s, pioneering microbiology studies began to reveal more about the composition of microbes on human skin. During this time much was learned regarding the identity of the dominant skin resident microorganisms under normal conditions and their association with disease. Typically, skin resident microorganisms are classified as those whose lifecycles are near permanently wedded to the skin (often referred to as skin resident or skin commensal microorganisms) and those which use the skin as a temporary conduit or transport mechanism by which to complete an aspect of their life cycle (the transient microbial population; for example, the role of hands as vectors for fecal or oral transmission of enteropathogenic Escherichia coli).

As the title of this chapter suggests, the focus will be on those resident or commensal microorganisms for which skin is their permanent home. These microorganisms derive their nutrients from skin, such as skin and sebaceous lipids or from other community members and the skin microenvironment determines local ecology and growth rate and limitation.

As will be discussed in more detail later, the ever-increasing accessibility of next generation sequencing techniques and their application to the field of microbiology continues to transform our understanding of the skin microbiome at a taxonomic and functional level. As this understanding grows, so does the need to embed those insights in an understanding of how local skin conditions (nutritional, microenvironmental, physical, chemical and immunological) impact the local microbial ecology, which may vary from the centimeter scale of occluded, non-occluded, sebaceous or non-sebaceous, hair or non-hairy body sites to the micron length scales of an individual hair follicle, eccrine gland or skin squame.

Pioneering work in the 1960s by Donald Pillsbury and Mary Marples laid essential groundwork for our understanding of how ecological constraints, such as the fundamental aridity of skin, affects what skin microorganisms. Later, work was done on the importance of skin lipids as nutrient sources and as natural antimicrobials [1–3]. This work helped to ground our understanding of how the normal processes of healthy skin modulates its microbiome by maintaining its local environment within narrow windows of pH, sebaceous activity, aridity, osmolarity and desquamation and how differences in these parameters help to explain the normally occurring differences in the microbiome between body sites [4–7].

That this is a two-way relationship, with microbes impacting skin condition and vice versa, was confirmed through seminal investigations by Roger Marples, Mary Stewart and others. These authors demonstrated how commensal skin microorganisms contribute to the normal functioning of healthy skin through the hydrolysis of sebaceous triglycerides into free fatty acids and glycerol, thereby contributing to the maintenance of normal skin acidity and hydration [8–13]. Such insights into the relationship between human lipids, their role as microbial nutrients and the impact on microbial localization to skin invaginations, such as hair follicles, were confirmed in light microscopy work by Montes [14]. More recently, the application of fluorescence in-situ hybridization (FISH) [15, 16] and cryosectioning scanning electron microscopy (SEM) techniques [17] have provided researchers with an unprecedented ability to visualize the spatial localization of microorganisms at the micron scale (Figure 1.1).

Figure 1.1 Use of an SEM image stack to visualise localisation of bacteria and yeast in a hair follicle. Reprinted with permission © Unilever.

However, despite the undoubted contribution of this work, it suffered from the limitations of laboratory culture techniques which restricted the organisms that could be detected and quantified to those that could be reproducibly cultured under laboratory conditions, and failed to capture the true diversity of the skin microbiome [18, 19].

1.1.2 Next Generation Sequencing

The advent of next generation sequencing techniques and advances in bio-informatics have transformed our understanding of the skin microbiome by tackling the reliance of the researcher on the agar plate as their sole tool in elucidating the composition of the skin’s microbial ecosystem.

Consequently, rather than simply culturing and examining a few microbial species at...