The germination of microecology at the end of the 19th century, which emerged in the 1970s, is the science of studying the interdependence and mutual constraints of human, animal and plant-dependent normal microflora. Many microbes live in the channels of the human body that communicate with the outside world. They have no harmful effects on the human body and are called normal flora. The normal flora community is in a dynamic equilibrium, which exists between different species, between the normal flora and the host, between the normal flora, the host and the environment. If there is a major change in the internal and external environment, this balance will be destroyed, and micro-ecological disorders will occur. If it cannot be adjusted in time, it will lead to various diseases in the host.
The number of microbes living in normal people is very large. It is estimated that the total number of normal microorganisms colonized in a healthy adult is about 1014, while in a normal adult there are about 1013 whole body cells. These microorganisms are mainly distributed in the skin, mouth, digestive tract, respiratory tract and genitourinary tract. . A considerable part of these microorganisms cause human diseases, but under normal circumstances, these parasites are safe and compatible with each other, and various microorganisms also restrict each other to maintain a state of equilibrium with each other.
The term probiotic comes from the Greek word “beneficial to life”. The United Nations Food and Agriculture Organization and the World Health Organization name probiotics: active microorganisms that are beneficial to the health of the host when given in sufficient amounts. Therefore, it can be considered that probiotics are necessary for the human body, such as lactic acid bacteria, and the lack or reduction will lead to the emergence of diseases. Most probiotics are selected based on experience, their safety is widely recognized through years of use, and is considered by the US Food and Drug Administration (FDA) to be “generally considered safe.” The probiotics currently used commercially are mainly Lactobacillus, Bifidobacterium, Pediococcus lactis and Streptococcus thermophilus. Lactic acid bacteria are a kind of probiotics widely distributed in the human body, mainly bacilli. The “longevity theory” of Nobel Prize winner Mitchinikov proposed: lactic acid bacteria = probiotics = longevity bacteria. Swedish scientists have also found that direct intake of lactic acid bacteria is better than antibiotics in the treatment of gastrointestinal inflammation, and side effects and risks are almost negligible.
The skin is the largest organ in the human body, colonizing complex microbial communities. Under the influence of the external environment that the epidermis is exposed to, the skin microbes form their unique and complex microbial structure, and are also affected by the innate immunity and the acquired immune system, and co-evolve with the human immune system. Along with the development of molecular biology, the complex and large resident bacteria on the skin are gradually recognized. An in-depth understanding of skin microbes not only helps people understand the interaction mechanism between microbes and skin barriers, but also provides an effective strategy for the treatment of microbial skin diseases.
The skin is the first barrier to isolate the environment and the external environment of the human body. The total skin area of adults is about 1.5 to 2.0 m2. Although the skin environment such as low temperature, dryness, high salt, acidity, presence of antimicrobial peptides, and flaking off the skin is not conducive to the growth and reproduction of microorganisms, there are still about 104 to 109 cells/cm 2 of microorganisms present on human skin. According to the length of time that different microorganisms are colonized on the surface of the skin, they can be divided into resident bacteria and temporary bacteria. The temporary colony has a short residence time on the surface of the skin and has less influence on the human body. It is generally a bacteria that is transmitted to the skin surface when the skin contacts the daily contact. The resident flora refers to long-term colonization on the skin, which has completely adapted to the skin environment and causes dependence. Such flora can be regarded as the core flora of the skin. Sebaceous glands and hair follicles are the main habitats of these resident flora, forming the first biological barrier of the skin, maintaining a balance and self-purification in the skin micro-ecological environment. The skin microbial flora structure of different individuals is also different. Studies have shown that the resident flora of the skin not only colonizes the surface of the skin, but also extends into the dermis. This indicates a very close relationship between the microorganisms and the body.
The resident bacteria of the skin mainly include Staphylococcus, Micrococcus, Propionibacterium, Corynebacterium, and Acinetobacter. The resident fungi include Candida, Saccharomyces cerevisiae, Epidermidis, Microsporum, Trichophyton. Common skin diseases caused by microbial infection include acne, allergic dermatitis, psoriasis, snake skin, oral hairy leukoplakia, bacterial hemangioma, and cellulitis. Through further research, researchers can clarify the characteristics of skin microbes and refine the whole skin microbial community to confirm the intrinsic relationship between human skin diseases and skin flora, and to be used in the diagnosis and treatment of skin diseases. .
1.Skin microbial difference
The most important factor affecting skin microbes is the environment, but the environment is a very complex and variable factor. First, the colonization host has strong individual differences, and different genotypes, ages, genders, living environment, living habits, and use of antibiotics are different. The skin bacteria on the back of the human body, the armpits and the soles of the feet are suitable to grow in a high temperature and high humidity environment, and are not suitable for a high temperature and low humidity environment. Gram-negative bacteria are suitable for proliferation in low-temperature and high-humidity skin environments, and at different latitudes and altitudes, bacterial proliferation may vary depending on the intensity of ultraviolet radiation. Another study found that the difference in resident flora between different single individuals is also very large. For example, the skin flora of female palms is much higher than that of males. In the same body, the structure of the flora of the left and right hands is also very different, which may involve daily hand habits, washing frequency, and the like. Studies have found that in areas where human facial oil secretion is strong, microbial diversity is low, and only a small number of specific bacteria are generally found. Staphylococcus and Propionibacterium are the dominant bacteria in these areas. In the relatively dry parts of human skin, the diversity of microbial flora structure is higher. In the areas of dry skin such as the forearm, waist, and hands, the complexity of the flora is often higher than that of the same individual’s intestines and mouth.
2.The effect of skin microbes on the human immune system
As the first line of defense of the human body, the symbiotic microorganisms on the skin can play an important role in preventing the host from invading the pathogenic bacteria. The microbial colonization process on the surface of newborn skin begins with childbirth. After birth, with the maturity of the immune system, the colonization of the microbial flora on the skin surface tends to be stable. The main colonizing bacteria in the early stages of human infants and young children is staphylococci, which is essential for the maturation of the human immune system. Symbiotic microorganisms can protect the body from pathogenic bacteria while stimulating the host’s immune system and enhancing its immunity. The colonization process of microorganisms is closely related to the pattern recognition receptors on the surface of the skin. Staphylococcus epidermidis is one of the resident bacteria in the skin, which inhibits the colonization and infection of pathogenic bacteria, and the wall of the bacteria itself can inhibit the occurrence of skin inflammation through the TLR2 and TLR3 signaling pathways in skin tissue. After infection, it can play a role in the survival and repair of cells.
3.Skin flora and skin diseases
If the immune regulation of the skin occurs, it will lead to various skin diseases such as atopic dermatitis. Leyden et al. (1974) found a correlation between atopic dermatitis and structural disorder on the surface of the skin. In recent years, further studies have shown that S. aureus infection is closely related to the onset of allergic dermatitis. Seborrheic dermatitis is a skin disease of fungal infection. It has been confirmed in the study of skin microbial culture in patients with seborrheic dermatitis that Malassezia is the main fungus leading to seborrheic dermatitis. In the process of maturation of adolescent facial hair follicle sebaceous glands, many lipophilic microorganisms are often colonized, secreting a large amount of lipase, protease and hyaluronidase, which damages normal tissues, causes local infection and inflammation, and eventually forms facial acne. In addition, skin microbes not only act on the surface of the skin, but also penetrate deeper into the dermis and even deeper layers. Microbiological studies on proliferating breast tissue have revealed that a large number of propionic acid bacteria are present in breast tissue, which may be closely related to breast tissue proliferation. Further microbiological studies on breast tumor specimens revealed that Methylbacteria is the dominant bacteria in the tumor site, and Sphingomonas is the dominant bacteria in normal tissue samples.
4.Probiotics and skin diseases
Healthy skin has its specific dominant flora. Once the skin flora is disordered, it will cause skin diseases such as atopic dermatitis, psoriasis and hemorrhoids. Previous treatments have used antibiotics, hormones and other drugs. Although these drugs can temporarily alleviate the symptoms of the disease, they often cannot completely eradicate the disease. If used for a long time, they may lead to side effects such as drug dependence and drug resistance. Therefore, microbial preparation therapy for restoring the normal stable state of the skin flora has gradually become a research hotspot. In recent years, with the gradual deepening of research on probiotics, it has been found that probiotics represented by Lactobacillus and Bifidobacteria not only have the ability to inhibit the propagation of pathogenic bacteria, but also improve the host’s own immunity and enhance the host’s invasion of pathogenic bacteria. resistance. At present, probiotics have gradually become a new generation of biological agents for the treatment of skin diseases, and have gradually had the potential to replace antibiotic treatment programs.
The study found that lactic acid bacteria can produce a large amount of organic acids, which can reduce the environmental pH, inhibit the growth of pathogenic bacteria, and reduce the pH of the environment can also activate macrophages, improve immune function, and enhance local anti-infection. ability. Lactic acid bacteria can also produce hydrogen peroxide, antibacterial peptides and bacteriocin, which also have a significant inhibitory effect on pathogenic bacteria. Therefore, in clinical applications, lactic acid bacteria are expected to become a mild fungicide in the future. At present, some probiotic skin care products have appeared in Europe and America, specifically for eczema, acne and sensitive skin problems. After use, skin sensitivity, inflammatory acne and other problems can be significantly improved. Through the regulation of skin micro-ecology, skin diseases are improved, and excellent anti-aging and facial rejuvenation are also made for long-term skin.
5.Intestinal flora and anti-aging
The intestinal flora is involved in many important physiological functions of the body, such as digestion of food, immune response and metabolism. Its variety and number are amazing, and it is called the “second genome” of human beings. According to statistics, the intestinal flora of a healthy adult can reach 1.0 to 1.5 kg. The intestinal flora is also divided into beneficial bacteria, harmful bacteria and intermediate bacteria. Beneficial bacteria are common bifidobacteria and lactobacilli, and harmful bacteria are spoilage bacteria. Studies have shown that bifidobacteria implantation in experimental rats can improve the lifespan of experimental rats and improve the health of aged rats. Studies have shown that with the increase of age, the spoilage bacteria in the human intestinal flora will increase year by year, and the spoilage bacteria will release harmful substances such as amines, botulinum toxin and hydrogen sulfide in the intestines, speeding up the aging process of the body; Beneficial bacteria such as lactobacilli and bifidobacteria in the tract will decrease with age. These studies show that the correlation between intestinal flora and human aging provides a theoretical basis for the future application of probiotics in anti-aging medicine.
American scientist Vanessa published a study in Science in 2013 that collects the feces of identically weighted identical twin women, or fat and thin identical twin women. They were then fed to sterile mice with no statistically significant differences, ie the “fat bacteria” and “lean bacteria” of identical twins were colonized in sterile mice, respectively. The two groups of mice were then fed the same low-fat, high-fiber feed. After feeding for a period of time, it was found that the mice that colonized the “fat bacteria” were significantly higher in weight than the mice that were colonized “skinny”. This case illustrates the presence of different gut flora in obese and lean individuals.
“Fecal bacteria transplantation” is to transplant functional bacteria in the feces of healthy people into the gastrointestinal tract of patients, and assist in the establishment of new intestinal flora to achieve treatment of diseases of the intestines and intestines. As early as 2012, the US Food and Drug Administration (FDA) positioned fecal transplants as a new treatment for certain diseases. In 2013, the United States first submitted a fecal transplant into clinical guidelines as an effective method to treat recurrent “C. difficile infection.” The treatment process of bacterial transplantation generally includes: colonoscopy, nasal feeding tube insertion, enema, and late capsule administration. However, the treatment plan needs to input the fecal bacteria into the intestine through a colonoscope or a catheter. The operation is somewhat traumatic, and the treatment process is relatively painful, which is difficult for many patients to accept, hindering its further promotion and application. Regarding the improvement of the treatment plan for the fecal transplant, there has been no stopping.
In short, after long-term exploration and research, there is increasing evidence that the balance of micro-ecology is closely related to human health. These resident bacteria in the skin and intestines help the body to improve its own immune system during the growth of the human body, maintain the stability of the flora structure, and also have a strong inhibitory effect on pathogenic bacteria. Therefore, it is necessary to maintain the balance of the skin and intestinal micro-ecological resident bacteria. Probiotics preparations are used to effectively intervene in the structure of the flora, thereby restoring the skin flora structure and micro-ecological balance in a healthy state; and the intestinal “fertilization” can effectively improve the balance of the intestinal flora and ultimately achieve therapeutic purposes. . Effective control of skin diseases has a direct impact on skin metabolism, nutrition, and regeneration, and is of great significance to skin anti-aging beauty. The study found that the microflora balance of intestinal flora is closely related to human aging. It is foreseeable that in the future research work, in-depth study of the skin and intestinal flora will open up a new way for the diagnosis and treatment of skin diseases, as well as anti-aging beauty and facial rejuvenation.