TESTING


The present and future of skin microbiome testing


Marco Piacentini, Anna Zugnoni – Eurofins


The skin is the largest organ of the human body and the one with the highest surface area, directly in contact with the external environment. This huge surface area harbours immune cells and it is inhabited by billions of resident commensal microorganisms constituting the so-called skin microbiota.1 The skin microbiota consists of the collection


of all microorganisms residing in an anatomical niche of the body, including bacteria, archaea, viruses and eukaryotes, while their genomes represent the skin microbiome, and its composition is unique to each person and part of the body.2,3


engaged in a continuous exchange with each other aiming to a dynamic balance.4 On the one hand, the skin provides


nutrients and abiotic factors (e.g. temperature and humidity) promoting microbiota growth. On the other hand, the microbiota prevents the colonisation of pathogens, directly and indirectly benefiting the host.5


Early-life microbiota The structure of human skin microbiome is formed during the early life stages, starting even before birth. It will then continuously evolve throughout the entire life cycle, impacted by multiple host-related and environmental factors. Birth marks a significant change for the skin


of the newborn transiting from the aqueous and mostly sterile environment of the womb into a gaseous one with constant microbial interactions.6


The early-life microbiota is


thought to be of considerable importance since it stimulates the development of the immune system, its maturation and development of immune tolerance. An important aspect relating to innate


immunity at birth is vernix caseosa. This waxy material covers the fetus skin during the last trimester of pregnancy and it facilitates extra-uterine adaptation of the skin post- birth. It moisturises infant skin, preserves its temperature and protects the infant during the early times after birth. Recent studies have shown vernix caseosa


contains antimicrobial peptides and lipids that are thought to protect the infant skin at the first contact with microbe’s ex utero and it is expected to play an important role in shaping the developing skin microbiome.7,8 Recently, it has been shown newborn skin


microbiome forming within 24 hours after birth strongly correlates with fetus delivery mode. In


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overcolonisation by the commensal bacteria Cutibacterium acnes. This gram-positive bacterium is the most


abundant cutaneous commensal of the human skin microbiome but it has been shown that some of its phylotypes have the potential to act as opportunistic pathogens and potentially lead to acne.11


Perturbations of the balance


within the dermal microbiome may compromise barrier function and are observed in various inflammatory skin disease besides acne, such as rosacea and atopic dermatitis (AD).


Microorganisms and host cells are


Role of atopic dermatitis AD is one of the most common non-contagious inflammatory skin disease and has a chronic recurrent course. Patients with atopic dermatitis are frequently colonized by Staphylococcus aureus, a gram-positive bacterium identified as an important disease-related pathogen. It has been shown that the degree of S. aureus colonization correlates with disease severity. This pathogen exacerbates the inflammatory


process and produce proteases and toxins that further weaken the already severely compromised barrier function of the skin of patients with AD. It is unclear if S. aureus is a cause of AD or a consequence of the abnormal epithelial environment.12


fact, naturally delivered neonates are showing a cutaneous bacterial signature, represented by community diversity and structure, resembling mother’s vaginal microbiota, with Lactobacillus predominating. Instead, neonates delivered by cesarean


are showing a skin microbiota resembling that of mother’s skin, including Staphylococcus, Corynebacterium, and Cutibacterium. Following this initial imprinting, during the following months, infant skin microbiota will increase its bio-diversity due to a reciprocal microbial transmission between mother and infant and an increasing contact with external environment. A gradual maturation of skin microbiome functions, structure, and composition occurs throughout the first years of life.9 In childhood, the major phyla retrieved


from children were similar to those found in adults, e.g. Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria, with essentially the same genera but at different ratios.10


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Therefore,


the mutualistic relationship between microbial communities and the host is essential for establishing the well-controlled and delicate balance needed for healthy skin. Emerging science demonstrates that the


microorganisms that colonise the skin surface play a decisive role in battling skin disease, maintaining skin immunity and supporting a healthy skin barrier. Nevertheless, because of the huge inter- and intra-individual variability in skin microbiota composition depending on the skin site it might result difficult to define how a healthy microbiota should look like. It seems that the healthy state of a tissue,


in which microbiome plays a role, is typically correlated with increased of the diversity of the species. In fact, it has been observed that disease states of a tissue are characterized by decreased microbial diversity compared to the healthy states.


During the transition through puberty,


sebum overproduction due to increased levels of androgenic hormones lead to a shift in the skin microbiome composition, with an


Species diversity concept The concept of species diversity has attracted the attention of the microbiome research community, above all the difference in meaning between the concept of richness and diversity.


November 2022 PERSONAL CARE


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