I often hear many people say: The skin must be washed clean, otherwise problems will occur! Parents who have babies with different skin at home often ask: Doctor, is it okay to just wash it with water? Can it be washed clean? There are a lot of bacteria on the skin! Is this really good? Most people believe that their skin should be germ-free and often use antibacterial cleaning products! But, here comes the question, is skin really sterile? Are bacteria necessarily harmful?
Conclusion: The skin is not sterile. An imbalance of good and bad bacteria causes disease.
Let’s talk about the conclusion first. The skin is not sterile. The microorganisms on the skin are quite rich. On average, one square meter There are more than 1 million bacteria per centimeter.
There are good and bad skin flora. The flora maintains normal skin physiological functions and trains the immune system.
Pathogenic bacteria can cause skin diseases, including: pustules, etc.
At the same time, different bacterial species on the skin will interact with each other, and they can synergistically benefit each other, and they can also be antagonistic to each other.
Therefore, bacterial balance plays an important role in maintaining normal skin physiological functions.
Next, let’s discuss in depth, what are skin microorganisms? What role does skin flora play?
Skin microorganisms are rich and important
Trillions of bacteria, molds, viruses, ancient cells and tiny arthropods live on the skin. The composition of these organisms forms the skin microbiome. /microbiota (skin microbiota).
We all know that the skin is the most important organ in contact with the outside world. It serves as a barrier between us and the external environment. It maintains moisture while also preventing external allergens, poisons, Pathogenic bacteria, and the invasion of ultraviolet rays.
However, skin is also home to millions of bacteria, molds, viruses, and even some arthropods.
The skin can be said to be a very harsh place for these microorganisms, because the skin is dehydrated, has few nutrients, and is a weakly acidic environment.
In addition, due to its differentiation, the skin will continue to slough off the surface, and at the same time it will shed the bacteria adhering to it, so microorganisms will face great difficulties in forming colonies on the skin. challenges.
Still, there are many different microbial colonies on the skin.
Microbial Identification Gene Sequencing
Traditionally, we have used culture to identify bacterial flora. However, according to statistics, less than 1 bacterial species can be borrowed. Grown with help from the laboratory.
The laboratory culture method actually only selects some specific bacterial species that can grow under specific nutritional and physiological conditions. This method may overly underestimate the diversity of the entire bacterial flora.
Therefore, in order to correct the errors caused by culture methods, scientists began to use a new method: gene sequencing.
Remove the tissue from the skin with a cotton swab, then extract its DNA, and use sequencing methods to identify the bacterial species.
This sequencing method uses the sequences conserved among these species. For example, bacterial genes all have 16s rRNA, which is used as the target of molecular gene map sequencing to identify members of the bacterial community, and finally You can tell which type of bacteria it is based on the sequencing results.
This method uses non-culture, gene sequencing methods to analyze collected microorganisms, which is called metagenomics. By identifying all species and relative amounts of bacteria, This allows us to have a complete understanding of the entire microbial ecological environment.
Human body: The number of bacteria is much greater than the number of cells
Human microbial colonies will exist on the skin surface and in the body.
An adult has up to one trillion bacteria, with a total weight of 1.3-1.5 kilograms, which is about the weight of the human brain and 10 times the number of cells in our entire human body. Therefore, we should not be humans, but walking bacteria. bacteria).
Beginning in 2007, the United States carried out the Genome Project to identify microbial colonies throughout the body and establish a database, hoping to further unravel the relationship between diseases and microbial colonies. ?
The microbial colonies of the skin include: bacteria, molds, viruses, and some arthropods.
The skin flora is also quite rich, with 1 million bacteria per square centimeter, which is quite a rich ecological area. Therefore, we will focus on the skin microbial flora next mainly on bacteria.
Skin microbial colonies: mainly bacteria
94% of the skin’s microbial colonies are prokaryotes, with bacteria being the largest group.
The skin flora has at least 19 phylum (Phylum), but four of them are dominant: Actinobacteria (51.8), Firmicutes (24.4), Proteobacteria (16.5) and Bacteroidetes (6.3).
If further analysis is carried out, the three most common genera are Corynebacteria spp., Propionibacteria spp. and Staphylocoi spp.
Skin flora is not constant
Does skin flora remain constant? In fact, this is not the case. There are many factors that affect the composition of skin flora. The first is personal physiological characteristics.
Different parts of the skin have different compositions of flora
In 2007, the American Human Genome Project investigated the flora of 242 normal healthy people, and analyzed the total number of skin parts in 20 parts. , it was found that the composition of skin flora was different in each part.
Further analysis found that the main reason is that different parts of the skin have different physiological characteristics, because the density of hair follicles, sweat glands, and sebaceous glands in each part is different, resulting in different skin surface environments and different bacterial flora compositions. .
Skin environment: oil, moisture, dryness
Skin can be mainly divided into three different ecological environments: oil, moisture, and dryness.
In areas with oily skin (Sebaceous skin), including the glabella, external auditory canal, sternum, back, etc., the main bacterial flora is Propionibacteria spp., because this type of bacteria is lipophilic , likes to live in a grease environment.
In areas with moist skin (moist skin), including armpits, inner elbows, groin, etc., the main bacterial flora are Corynebacteria spp. and Staphylococcus spp.
Dry skin (Dry skin) areas include the inner forearms and palms, which are mainly mixed bacteria.
Surprisingly, many Gram-negative bacteria, previously thought to live mainly in the gastrointestinal tract, have also been found to live in areas with dry skin.
Different individuals have similar flora in the same part.
In addition, when we examined different people, we also found that the composition of the flora in the same part was similar between different people.
In contrast, the composition of bacterial flora in different parts of the same person is quite different.
From this study, it can be found that the location of the skin (ecological environment) is a more decisive factor in the composition of the bacterial flora than the genetic differences between individuals.
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In addition to different parts of the skin affecting the composition of the bacterial flora, is the composition of the bacterial flora consistent from birth to old age?
At birth, the newborn's bacterial flora is quite consistent, and the skin flora composition of the entire body is similar.
The method of production determines the composition of the newborn's skin flora. If it is through the birth canal, there will be mother's bacterial colonies, mainly lactic acid bacteria (Lactobacillus).
If it is a caesarean section, the flora will be similar to the mother's skin.
The flora will then begin to slowly evolve with age.
Is the composition of the bacterial flora different at different ages?
The skin flora will continue to change in the first year after birth. At the same time, compared with adults, infant skin is mainly composed of Firmicutes. (Firmicutes phylum) is the main flora, that is, Staphylococcus (Staphylocous spp.) and Streptococcus (Streptocous spp.) are the main flora.
For newborns aged 1-3 months and 4-6 months old, Staphylococcus spp. and Streptococcus spp. account for 40% of the skin flora, being the two most abundant. Plant flora.
As babies get older, the number of Staphylococcus spp. and Streptococcus spp. will decrease significantly, while other bacterial groups will increase by the time they are 7-12 months old. , which explains the development and variability of the skin microbiota. ?
This study also found that when infants are 4-6 months old, the number of Propionibacteria spp. in the forehead will suddenly increase significantly, and this period is when infantile acne occurs. At the age when acne is more likely to occur, it can be seen that there is a correlation between skin flora and skin diseases.
In addition, if we look at the age range, after puberty, due to increased sebum secretion and changes in the skin's physiological environment, it will help the growth of lipophilic flora. As can be seen from the picture above, acne bacteria and Corynebacterium increases significantly from adolescence onwards.
It was also found that the genus Streptococcus gradually decreased with age.
In addition, Staphylococcus epidermidis (S. epidermidis), a common bacteria in the skin flora, increases with age.
The most common pathogen, Staphylococcus aureus (S. aureus), can be found in 20.6 healthy people, but its content in all age groups is very low, less than 1%.
This study also observed that during adolescence, as children prepare to become adults, the skin flora is also changing, and it is highly similar to the adult flora.
Both genes and environment affect the composition of skin flora.
In addition to the physiological environment of the skin, genes also affect the composition of our flora.
Research has also found that mutations in the filaggrin gene are related to skin flora.
Patients with filaggrin gene deficiency have higher levels of Staphylococcus aureus in their skin flora.
The skin contact environment is also related to the skin flora, because the moisture content and pH level of the skin also affect the composition of the flora.
The weakly acidic environment of the skin will inhibit the reproduction of pathogenic bacteria (Pathogen colonization), and pH5.5 will inhibit the growth of Staphylococcus aureus (S. aureus).
At the same time, although an acidic environment will inhibit the growth of Staphylococcus aureus, Staphylococcus epidermidis (S. epidermidis) will grow better at a pH of 4.7 than in a pH of 7.0. .
Taken together, the skin’s physiological environment, genes and exposure environment all have an impact on the composition of the bacterial flora.
After introducing these bacterial flora, what role do these bacterial flora play on the skin? It shouldn’t be as simple as just treating the skin as a big platform for growth! ? Will it also provide us with some benefits? ?
Skin flora interaction
First of all, research has found that flora communicate with each other and do not just grow together. The accumulation of microbial flora is not only affected by the host. , the bacteria will also interact with each other. Microorganisms can compete with each other to eliminate other bacteria, or they can work together to benefit each other.
Staphylococcus aureus is the target of other bacterial flora
On the skin, Staphylococcus aureus (S. aureus) has always been the focus of research, especially in atopic dermatitis As for the patient, in fact, he is also the focus of attack by other bacterial species!
It interacts with many common skin flora, including: S. lugdunensis, S. hominis, S. epidermidis and P. acnes (P. aes).
1. Staphylococcus lugdunensis (S. lugdunensis) produces an antibiotic (Lugdunin) to inhibit the growth of Staphylococcus aureus. More importantly, after long-term treatment, despite several generations of evolution, Staphylococcus aureus Staphylococcus aureus has not developed resistance to lugdunin, which is very different from traditional antibiotics. It can be seen that naturally derived substances are more effective than antibiotics in inhibiting pathogenic bacteria.
2. Staphylococcus hominis (S. hominis) produces an antibiotic (Lantibioitcs) that can work with the antibacterial peptide (LL-37) secreted by the skin to inhibit Staphylococcus aureus growth, and also found that patients with atopic dermatitis lack strains that produce lantibioITCs, especially those who suffer from repeated infections with Staphylococcus aureus.
3. Staphylococcus epidermidis (S. epidermidis) produces serine protease glutamyl endopeptidase (Esp), which can inhibit the formation of Staphylococcus aureus biofilm.
4. P. acnes (P. aes) can produce a small molecule Coproporphyrin III, which can aggregate Staphylococcus aureus and help its biofilm formation.
5. A study found that when Staphylococcus aureus comes into contact with a common bacteria, Corynebacterium striatum, it changes its behavior from a pathogenic bacteria to a resident bacteria (Corynebacterium striatum). Virulent to Commensal). The ability to change the behavior of Staphylococcus aureus also opens up an alternative approach to treating disease by changing the bacteria's behavior rather than destroying the pathogenic bacteria.
Skin flora affects skin immunity
In addition to the interaction between flora, skin flora also interacts with the human body, that is, the host.
Keratinocytes secrete antibacterial peptides, which are our most important weapons against microorganisms.
Although some antimicrobial peptides are continuously expressed, some antimicrobial peptides are controlled by specific microorganisms. For example, Staphylococcus epidermidis (S. epidermidis) can prompt keratinocytes to secrete antimicrobial peptides, so that The flora is beneficial to the skin.
More and more studies now confirm that probiotics are already present on the skin surface and are part of the innate immune system.
Staphylococcus epidermidis (S. epidermidis) can regulate the innate immune inflammatory response, induce antigen presenting cells (APC) to produce a cytokine (IL-10) to suppress inflammation, and can also increase T cells Gather in the skin and affect T cell maturation.
At the same time, the host's immune response also affects the microbial flora.
Current evidence suggests that the skin flora plays an important role in educating and helping the maturation of the immune system, whether it is the innate or acquired immune system.
Conclusion The skin is not sterile and the sterile flora cannot affect immunity
The skin is not a sterile environment as we originally thought. On the contrary, the skin flora is quite rich and plays a role in important role.
Bacteria often interact with each other on the skin and can also affect the body's immune response.
The normal flora can inhibit the reproduction of pathogenic flora and reduce the occurrence of skin diseases. Maintaining the balance of skin flora is very important for the normal physiological functions of the skin.
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