Added: Zarinah Moors - Date: 11.09.2021 00:56 - Views: 26353 - Clicks: 3089
Try out PMC Labs and tell us what you think. Learn More. 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 is an ecosystem composed of 1. The primary role of the skin is to serve as a physical barrier, protecting our bodies from potential assault by foreign organisms or toxic substances. The skin is also an interface with the outside environment and, as such, is colonized by a diverse collection of microorganisms — including bacteria, fungi and viruses — as well as mites 1 — 7 FIG. As we describe, many of these microorganisms are harmless and in some cases provide vital functions that the human genome has not evolved.
Symbiotic microorganisms occupy a wide range of skin niches and protect against invasion by more pathogenic or harmful organisms.
These microorganisms may also have a role in educating the billions of T cells that are found in the skin, priming them to respond to similarly marked pathogenic cousins. Microorganisms viruses, bacteria and fungi and mites cover the surface of the skin and reside deep in the hair and glands.
On the skin surface, rod and round bacteria — such as Proteobacteria and Staphylococcus spp. Commensal fungi such as Malassezia spp. Virus particles live both freely and in bacterial cells. Skin mites, such as Demodex folliculorum and Demodex brevisare some of the smallest arthropods and live in or near hair follicles. Skin appendages include hair follicles, sebaceous glands and sweat glands. The perception of the skin as an ecosystem — composed of living biological and physical components occupying diverse habitats — can advance our understanding of the delicate balance between host and microorganism.
Disruptions in the balance on either side of the equation can result in skin disorders or infections. Perturbations affecting the host—microorganism relationship can be endogenous for example, genetic variation that selects for a specific microbial community or exogenous for example, hand washing.
To further our understanding of health, disease and infection of the skin, microbiologists, immunologists and dermatologists have partnered with genomic scientists to develop a more complete characterization of the skin microbiota and how it interacts with the host FIG.
Exogenous and endogenous factors discussed in this Review that contribute to variation between individuals and over the lifetime of an individual. The physical and chemical features of the skin select for unique sets of microorganisms that are adapted to the niche they inhabit.
In general, the skin is cool, acidic and desiccated, but distinct habitats are determined by skin thickness, folds and the density of hair follicles and glands 8. Structurally, the epidermis is a formidable physical barrier, resisting penetration by microorganisms and potential toxins while retaining moisture and nutrients inside the body 9 — The top layer of the epidermis, the stratum corneum FIG. Cutaneous invaginations and appendages, including sweat glands eccrine and apocrinesebaceous glands and hair follicles, are likely to be associated with their own unique microbiota 13 FIG.
Eccrine glands, which are more abundant than apocrine glands, are found on virtually all skin surfaces and continuously bathe the skin surface with their secretion, which is composed mainly of water and salt. The primary role of eccrine sweat is thermoregulation through the release of latent heat from the evaporation of water. Additional functions of eccrine glands include excretion of water and electrolytes, and acidification of the skin, which prevents the colonization and growth of microorganisms. Apocrine glands, which are located in the axillary vault armpitnipple and genitoanal regions, respond to adrenaline by producing milky, viscous, odourless secretions.
Apocrine secretions have long been postulated to contain pheromones, which are molecules that trigger certain behaviours for example, sexual or alarm in the receiving individual The stereotypical odour associated with sweat derives from bacterial processing and utilization of apocrine gland secretions 15 — Sebaceous glands are connected to the hair follicle, forming the pilosebaceous unit, and secrete the lipid-rich substance sebum.
Sebum is a hydrophobic coating that protects and lubricates the skin and hair and provides an antibacterial shield. Sebaceous glands are relatively anoxic and support the growth of facultative anaerobes such as Propionibacterium acnesa common skin commensal bacterium 3 Full genome sequencing of P. The bacterium can then adhere to these free fatty acids, and this perhaps aids in the colonization of the sebaceous gland Many common pathogens, such as Staphylococcus aureus and Streptococcus pyogenes, are inhibited by an acidic pH, thus the growth of coagulase- negative staphylococci and corynebacteria is favoured 1023 — However, skin Layer of the skin dating online good things in an elevated pH, which favours the growth of S.
Because humans produce much greater quantities of triglyceride-containing sebum than other mammals, P. The skin surface varies topographically owing to regional differences in skin anatomy and, according to culture-based studies, these regions are known to support distinct sets of microorganisms. Some regions of the skin are partially occluded, such as the groin, axillary vault and toe web. These regions are higher in temperature and humidity, which encourages the growth of microorganisms that thrive in moist conditions for example, Gram-negative bacilli, coryneforms and S.
The density of sebaceous glands is another factor that influences the skin microbiota, depending on the region.
Areas with a high density of sebaceous glands, such as the face, chest and back, encourage the growth of lipophilic microorganisms for example, Propionibacterium spp. Compared with other skin sites, arm and leg skin is relatively desiccated and experiences large fluctuations in surface temperature. Using culture-based methods, these areas were found to harbour quantitatively fewer organisms than moist areas of the skin surface 3. Factors specific to the host, such as age, location and sex, contribute to the variability seen in the microbial flora of the skin FIG. Age has a great effect on the microenvironment of the skin and, thus, on the colonizing microbiota 27 In uterofetal skin is sterile, but colonization occurs immediately after birth, either during vaginal delivery or in the minutes following birth by caesarian section 29 One area for future research is to explore how the microbial communities of the skin and other sites are established and stabilized during the first years of life, Layer of the skin dating online good things a newborn baby explores its environment and matures its immune system During puberty, changes in sebum production parallel the levels of lipophilic bacteria on the skin, as determined by culture-based approaches Physiological and anatomical differences between male and female cutaneous environments such as sweat, sebum and hormone production, partially for the microbial differences seen between the genders 32 — Environmental factors specific to the individual, such as occupation, clothing choice and antibiotic usage, may modulate colonization by the skin microbiota FIG.
The effect of antibiotic treatment on the gut microbiota has been examined using molecular methods 35 — 37 but, to our knowledge, a similar assessment of skin microbiota in healthy individuals does not exist. Cosmetics, soaps, hygienic products and moisturizers are also potential factors contributing to the variation of skin microbiota. These products alter the conditions of the skin barrier but their effects on skin microbiota remain unclear.
Quantitative culture demonstrated that high-temperature and high-humidity are associated with increased quantities of bacteria on the back, axillary vaults and feet as compared with high-temperature low-humidity conditions In the same study, high humidity and low temperature conditions were associated with a higher frequency of Gram-negative bacteria on the back and feet. Genomic approaches to characterize skin bacteria have revealed a much greater diversity of organisms than that revealed by culture-based methods 3340 — 43 BOX 1.
As defined by 16S ribosomal RNA metagenomic sequencingmost skin bacteria fall into four different phyla: Actinobacteria, Firmicutes, Bacteroidetes and Proteobacteria. These four dominant phyla also constitute the microbiota that is found on the inner mucosal surfaces the gastrointestinal tract and oral cavity 44 — However, the proportions differ vastly: whereas Actinobacteria members are more abundant on skin, Firmicutes and Bacteroidetes members are more abundant in the gastrointestinal tract.
A common feature of gut and skin microbial communities seems to be low diversity at the phylum level, but high diversity at the species level. Microorganisms colonizing the skin have long been of interest to dermatologists and microbiologists; our knowledge of these microorganisms has, until recently, been gleaned through culture-based studies.
Historically, Staphylococcus epidermidis and other coagulase-negative staphylococci have been regarded as the primary bacterial colonizers of the skin. Other microorganisms that are generally regarded as skin colonizers include coryneforms of the phylum Actinobacteria the genera Corynebacterium, Propionibacterium and Brevibacterium and the genus Micrococcus. Gram-negative bacteria, with the exception of some Acinetobacter spp.
Non-bacterial microorganisms have also been isolated from the skin. The most commonly isolated fungal species are Malassezia spp. The Demodex mites such as Demodex folliculorum and Demodex breviswhich are microscopic arthropods, are also regarded as part of the normal skin flora. Demodex mites feed on sebum and are more prevalent following puberty, preferring to colonize sebaceous areas of the face 3.
Demodex mites may also feed on epithelial cells lining the pilosebaceous unit, or even on other organisms such as Propionibacterium acnes that inhabit the same space. The role of commensal viruses has not been studied, and investigations are limited by the available molecular and microbiological means to identify and characterize viruses. Historically, culture-based approaches have been the standard for characterizing microbial diversity. It is now evident that only a minority of bacteria are able to thrive in isolation These are not necessarily the most abundant or influential organisms in the community.
This bias is especially apparent when attempting to isolate skin microorganisms, which are inherently adapted to a cool, dry and acidic environment. Furthermore, hair follicles and sebaceous glands are anoxic environments and harbour anaerobic microorganisms.
Isolation of anaerobes is particularly problematic using routine culture-based approaches These organisms are often slow growing and require special conditions for growth and during sample transport and processing. The development of molecular techniques to identify and quantify microbial organisms has revolutionized our view of the microbial world.
Genomic characterization of bacterial diversity relies on sequence analysis of the 16S ribosomal RNA gene, which is present in all bacteria and archaea but not in eukaryotes. The 16S rRNA gene contains species-specific hypervariable regions, which allow taxonomic classification, and highly conserved regions, which act as a molecular clock and a binding site for PCR primers The advent of new sequencing technologies such as pyrosequencing has massively increased throughput while decreasing the cost of sequencing.
Importantly, an organism does not need to be cultured to determine its type by 16S rRNA sequencing. Molecular approaches examining bacterial diversity have underlined the concept that the skin microbiota is dependent on the body site and that caution should be taken when selecting and comparing sites for skin microbiome studies. Our group and others have demonstrated that colonization of bacteria is dependent on the physiology of the skin site, with specific bacteria being associated with moist, dry and sebaceous microenvironments FIG. In general, bacterial diversity seems to be lowest in sebaceous sites, suggesting that there is selection for specific subsets of organisms that can tolerate conditions in these areas.
Sebaceous sites that contain low phylotype richness include the forehead six phylotypes 43the retroauricular crease behind the ear 15 phylotypes 42the back 17 phylotypes 42 and the alar crease side of the nostril 18 phylotypes Propionibacterium spp. Microbial transplant experiments suggest that the microenvironment of sebaceous areas such as the forehead is a stronger force in determining microbial colonization than the microenvironment of dry areas such as the forearm The skin microbiome is highly dependent on the microenvironment of the sampled site.
The family-level classification of bacteria colonizing an individual subject is shown, with the phyla in bold. The sites selected were those that show a predilection for skin bacterial infections and are grouped as sebaceous or oily blue circlesmoist typically skin creases green circles and dry, flat surfaces red circles.
The sebaceous sites are: glabella between the eyebrows ; alar crease side of the nostril ; external auditory canal inside the ear ; retroauricular crease behind the ear ; occiput back of the scalp ; manubrium upper chest ; and back.Layer of the skin dating online good things
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