SKIN MICROBIOME
Microbiome claims: to do or not to do?
Dr Ernesta Malinauskyte, Dr Marcella Gabarra Almeida Leite – TRI Princeton, US
There is an ongoing debate regarding microbiome terminology in the microbiology field.1
In this
paper, we will be using the following definitions: (i) Microbiota is defined as the live (or active) microorganisms present on the body, and (ii) microbiome is the community of these microorganisms and the ones that are not considered alive (phages, viruses, plasmids, prions, viroids, and free DNA), their environment and interaction amongst each other and their host.1
An additional difference between these two
terms can be explained by how we study them. Microbiota can be studied separately from their natural environment (in vitro studies) however, the environment of microbiome studies must include all members of the microbiological “community” within its natural habitat1
despite that our interest
might be only one strain. The microbiome is frequently evaluated while studying the genome of the microorganisms of interest. The microbiome is first formed when the
newborn’s skin first makes a contact with the mother. The newborn’s digestive tract and skin become colonised by the mother’s microorganisms which will later become part of its microbiome. This process is associated with the development and stimulation of the immune system.2
While studies show that the
gut microbiome can influence the skin, in this paper, we will focus primarily on the relationship between skin microbiome and skin health. There are two types of microorganisms on the skin, the resident (commensal) and the transient. The commensal microorganisms reside on human skin throughout human life. Due to occasional perturbation, they might leave the skin, but will repopulate again. Meanwhile, the transient ones are not permanent, usually persisting for hours or days due to external conditions.3
The skin,
along with these microorganisms, consists of a protective system against external aggressions. There is a balance in the composition of the skin’s components, called hydrolipidic balance, and the microbiome has its own balance that is established by a variety of healthy skin microorganisms networking with each other and the skin. When external factors promote alterations in any of these equilibria, dysbiosis occurs, making the skin more susceptible to the development of pathologies.4
Therefore, it is
important to understand how the skin and its external conditions can affect the microbiome homeostasis and consequently promote alterations in the skin.
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How microbiome differs between body regions The skin presents a more diverse number of bacterial colonies than other organs or gland surfaces. In decreasing order, the level of research performed on other types of microorganisms is as follows: fungi, arthropods (mites), and viruses. The principal fungi present on the skin is Malassezia, representing some 80% of the fungi on the surface, especially the scalp. Demodex is identified as the primary type of mites that reside in hair follicles and sebaceous glands.5 viruses is still scarce,4
(the most frequently mentioned in the literature being Papillomaviridae, Polyomaviridae and Circoviridae.6 The position of the skin on the body is
a major factor contributing to microbiome diversity.7
Skin on different parts of the
The research regarding skin although it is worth noting
that skin viriome consists of (a) bacterial viruses (the most abundant being Cutibacterium and Staphylococcus phages) and (b) human viruses
body possesses unique characteristics that are favourable to specific microorganisms because of differences in temperature, acidity, thickness, hair density, produced sebum and moisture levels. The changes in any of these characteristics tend to contribute to the alterations in the microbiome.3, 4, 8 For example, occluded areas such as armpits
present higher temperature and humidity, leading to growth of Gram-negative bacteria – Staphylococcus, Micrococcus, Corynebacterium. and Cutibacterium. Regions with a higher number of sebaceous glands as facial skin and scalp can lead to the growth of lipophilic microorganisms such as Cutibacterium and Malassezia.3, 4, 8
Dry regions such as the forearm
tend to contain larger microbial diversity, while the lowest diversity was found in the scalp, armpits, and other moist skin regions.7, 9 Skin appendages such as sweat glands,
sebaceous glands, and hair follicles also have their own relatively isolated microbiota. The environment in hair follicle is moist, less acidic, rich in sebum, and well protected from UV radiation which enables favorable conditions for a variety of microorganisms.10
Because hair follicles and sebaceous glands are connected, September 2021 PERSONAL CARE
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