Negative significance of microflora.
Normal microflora of the human body and its meaning. The concept of gnotobiology. Disbiosis. Preparations used to restore normal microflora. In a healthy animal, the internal tissues, e. g. blood, brain, muscle, etc., are normally free of microorganisms. On the other hand, the surface tissues, e. g. skin and mucous membranes, are constantly in contact with environmental organisms and become readily colonized by certain microbial species. The mixture of organisms regularly found at any anatomical site is referred to as the normal flora. The normal flora of humans is exceedingly complex and consists of more than 200 species of bacteria. The makeup of the normal flora depends upon various factors, including genetics, age, sex, stress, nutrition and diet of the individual. The normal flora of humans consists of a few eukaryotic fungi and protists, and some methanogenic Archaea that colonize the lower intestinal tract, but the Bacteria are the most numerous and obvious microbial components of the normal flora. Very little is known about the nature of the associations between humans and their normal flora, but they are thought to be dynamic interactions rather than associations of mutual indifference. Both host and bacteria are thought to derive benefit from each other, and the associations are, for the most part, mutualistic. The normal flora derives from the host a supply of nutrients, a stable environment and constant temperature, protection, and transport. The host obtains from the normal flora certain nutritional benefits, stimulation of the immune system, and colonization strategies that exclude potential pathogens at the site. The composition of the normal flora The normal flora of corresponding anatomical sites in different animal species varies widely. Within a single species (e. g. humans) there is additional variation in the normal flora that is related to factors such as age, sex, diet and nutrition. Some bacteria are found regularly at particular anatomical locales; others are present only occasionally, or at certain times during life. Developmental changes in humans such as weaning, the eruptions of the teeth, and the onset and cessation of ovarian functions, invariably affect the composition of the normal flora in the intestinal tract, the oral cavity, and the vagina, respectively. However, within the limits of these fluctuations, the bacterial flora of humans is sufficiently constant to a give general description of the situation. It has been calculated that the normal human houses about 1012 bacteria on the skin, 1010 in the mouth, and 1014 in the gastrointestinal tract. The latter number is far in excess of the number of eukaryotic cells in all organs which comprise the human host. Normal flora of the skin. The adult human is covered with approximately 2 square meters of skin. The density and composition of the normal flora of the skin vary with anatomical locale. The high moisture content of the axilla, groin, and areas between the toes supports the activity and growth of relatively high densities of bacterial cells, but the density of bacterial populations at most other sites is fairly low, generally in 100s or 1000s per square cm. Qualitatively, the bacteria on the skin near any body orifice may be similar to those in the orifice. The majority of skin microorganisms are found in the most superficial layers of the epidermis and the upper parts of the hair follicles. They consist largely of micrococci (S. epidermidis and Micrococcus spp. ) and corynebacteria. These are generally nonpathogenic and considered to be commensal, although mutualistic and parasitic roles have been assigned to them. Sometimes potentially pathogenic Staphylococcus aureus is found on the face and hands, particularly in individuals who are nasal carriers. The skin has a bactericidal action (destruction of microbes). The bactericidal effect is due to the content of antimicrobial agents in the sweat: a-globulins, immunoglobulins A, transferrin, lysozyme, etc. This action is more effective if the skin is clean. On dirty skin, there is an increase in the growth of microorganisms, which determine the smell of the body. The microflora of the skin is of great importance in air pollution by microorganisms. This happens when the skin is peeling, as microorganisms are on the scales. Through dirty hands: 1) contamination of medicinal products by microorganisms can occur, which cause their spoilage; 2) transmission of infections (gastrointestinal tract, skin) by contact way can occur. The sanitary-indicative bacteria of the skin are: 1) E. coli; 2) Streptococcus faecalis; 3) Staphylococcus aureus. Microbiological investigation of the skin is inoculation of the washing from the skin. Normal flora of the respiratory tract. The nares (nostrils) are always heavily colonized, predominantly with S. epidermidis and corynebacteria, and often (about 20% of the general population) with S. aureus, this being the main carrier site of this important pathogen. The healthy sinuses, in contrast are sterile. A large number of bacterial species colonize the upper respiratory tract (nasopharynx). The predominant species are non-hemolytic and alpha- hemolytic streptococci and Neisseria spp., but sometimes pathogens such as S. pneumoniae, S. pyogenes, H. influenzae and N. meningitidis colonize the pharynx. The lower respiratory tract (trachea, bronchi, and pulmonary tissues) are virtually free of microorganisms, mainly because of the efficient cleansing action of the ciliated epithelium which lines the tract. Any bacteria reaching the lower respiratory tract are swept upward by the action of the mucociliary blanket that lines the bronchi, to be removed subsequently by coughing, sneezing, swallowing, etc. If the respiratory tract epithelium becomes damaged, as in bronchitis or viral pneumonia, the individual may become susceptible to infection by pathogens descending from the nasopharynx (e. g. H. influenzae or S. pneumoniae). The pathogen Bordetella pertussis is specifically able to colonize the tracheal epithelium of humans, allowing it to produce the disease, pertussis (whooping cough). Normal flora of the human oral cavity. The presence of nutrients, epithelial debris, and secretions makes the mouth a favorable habitat for a great variety of bacteria. Oral bacteria include streptococci, lactobacilli, staphylococci and corynebacteria, with a great number of anaerobes, especially Bacteroides. The mouth presents a succession of different ecological situations with age, and this corresponds with changes in the composition of the normal flora. At birth the oral cavity is sterile but rapidly becomes colonized from the environment, particularly from the mother in the first feeding. S. salivarius is dominant and may make up 98% of the total oral flora until the appearance of the teeth (6-9 months in humans). The eruption of the teeth during the first year leads to colonization by S. mutans and S. sanguis. These bacteria require a nonepithelial surface in order to colonize. They will persist as long as teeth remain. Other strains of streptococci adhere strongly to the gums and cheeks but not to the teeth. The creation of the gingival crevice area (supporting structures of the teeth) increases the habitat for the variety of anaerobic species found. The complexity of the oral flora continues to increase with time, and Bacteroides spp. and spirochetes colonize around puberty. The main role in the formation of microflora is played by saliva, which has bactericidal properties (lysozyme, lactoferrin, peroxidase, nuclease, Ig A). Clearly, the normal bacterial flora of the oral cavity benefit from their associations with their host. Are there benefits as well to the host? Perhaps. The normal flora occupies available colonization sites which makes it more difficult for other microorganisms (nonindigenous species) to become established. Also, the oral flora contributes to host nutrition through the synthesis of vitamins, and they contribute to immunity by inducing low levels of circulating and secretory antibodies that may cross react with pathogens. Finally, the oral bacteria exert microbial antagonism against nonindigenous species by production of inhibitory fatty acids, peroxides, bacteriocins, etc. The oral flora of humans may harm their host since some of these bacteria are parasites or opportunistic pathogens. The microflora of the oral cavity is one of the reasons of caries. If certain oral bacteria are able to invade tissues not normally accessible to them, characteristic diseases result. For example, oral organisms gaining entrance into tissues (e. g. via surgical wounds) may cause abscesses of alveolar bone, lung, brain or the extremities. Such infections usually contain mixtures of bacteria with Prevotella spp. and Porphyromonas spp. often playing a dominant role. Also, oral streptococci may be introduced into wounds created by dental manipulation or treatment. If this occurs in an individual with damaged heart valves due to rheumatic fever (previously induced by streptococci), the oral streptococci may adhere to the damaged heart valves and initiate subacute bacterial endocarditis. Normal flora of the gastrointestinal (GI) tract The bacterial flora of the GI tract of animals has been studied more extensively than that of any other site. The composition differs between various animal species, and within an animal species. In humans, there are differences in the composition of the flora which are influenced by age, diet, cultural conditions, and the use of antibiotics. The latter greatly perturbs the composition of the intestinal flora. In the upper Gl tract of adult humans, the esophagus contains only the bacteria swallowed with saliva and food. Because of the high acidity of the gastric juice very few bacteria (mainly acid-tolerant lactobacilli) can be cultured from the normal stomach. However, a substantial proportion of population is colonized by a pathogenic bacterium, Helicobacter pylori. Since the 1980s, this bacterium has been known to be the cause of gastric ulcers, and it is a cause of gastric and duodenal cancer as well. The proximal small intestine has a relatively sparse Gram-positive flora, consisting mainly of Iactobacilli and Enterococcus faecalis. This region has about 105-107 bacteria per ml of fluid. The distal part of the small intestine contains greater numbers of bacteria (108/ml) and additional species including coliforms and Bacteroides spp., in addition to lactobacilli and enterococci. The flora of the large intestine (colon) is qualitatively similar to that found in feces. Populations of bacteria in the colon reach levels of 1011/ml feces. Coliforms become more prominent, and enterococci, clostridia and lactobacilli can be regularly found, but the predominant species are anaerobic Bacteroides spp. and anaerobic lactic acid bacteria in the genus Bifidobacterium (Bifidobacterium bifidum). These organisms may outnumber E. coli by 1, 000: 1 to 10, 000: 1. It is now known that significant numbers of anaerobic methanogenic bacteria (up to 1010/g) also reside in the colon of humans. At birth the entire intestinal tract is sterile, but bacteria enter with the first feed. The initial colonizing bacteria vary with the food source of the infant. In breast-fed infants bifidobacteria account for more than 90% of the total intestinal bacteria. Enterobacteriaceae and enterococci are regularly present, but in low proportions, while bacteroides, staphylococci, lactobacilli and clostridia are practically absent. In bottle-fed infants, bifidobacteria are not predominant. When breast-fed infants are switched to a diet of cow’s milk or solid food, bifidobacteria are progressively joined by enterics, bacteroides, enterococci lactobacilli and clostridia. Apparently, human milk contains a growth factor that enriches for growth of bifidobacteria, and these bacteria play an important role in preventing colonization of the infant intestinal tract by non indigenous or pathogenic species. The composition of the flora of the GI tract varies along the tract (at longitudinal levels) and across the tract (at horizontal levels) where certain bacteria attach to the gastrointestinal epithelium and others occurs in the lumen. There is frequently a very close association between specific bacteria in the intestinal ecosystem and specific gut tissues or cells (evidence of tissue tropism). Many bacteria adhere specifically to the gastrointestinal epithelial surfaces, and this has been shown in many animal species including humans, cows, dogs, pigs, mice and chickens. Gram-positive bacteria, such as the streptococci and lactobacilli, are thought to adhere to the gastrointestinal epithelium using polysaccharide capsules or wall lipoteichoic acids to attach to specific receptors on the epithelial cells. Likewise, Gram-negative bacteria such as the enterics may attach by means of specific fimbriae on the bacterial cell which bind to glycoproteins on the epithelial cell surface. The benefits of the normal flora The indigenous bacteria of the gastrointestinal tract of an animal, perhaps mainly as a consequence of their great numbers, seem to have the greatest overall impact on their host. The nature of the interactions between an animal host and its normal flora has been inferred from the study of germ-free animals (animals which lack any bacterial flora) compared to conventional animals (animals which have a typical normal flora). The science of the non-microbial life of animals is called gnotobiology. Following are the primary beneficial effects of the normal flora that are derived from this science. 1. The normal flora synthesizes and excretes vitamins in excess of their own needs, which can be absorbed as nutrients by the host. For example, enteric bacteria secrete vitamin К and vitamin B]2, and lactic acid bacteria produce certain В vitamins. Germ-free animals may be deficient in vitamin К to the extent that it is necessary to supplement their diets. 2. The normal flora prevents colonization by pathogens (colonization resistance) by competingfor attachment sites or for essential nutrients. This is thought to be their most important beneficial effect, which has been demonstrated in the oral cavity, the intestine, the skin, and the vaginal epithelium. In some experiments, germ-free animals can be infected by 10 Salmonella, while the infectious dose for conventional animals is near 106 cells. 3. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species. The intestinal bacteria produce a variety of substances ranging from relatively nonspecific fatty acids and peroxides to highly specific bacteriocins, which inhibit or kill other bacteria. 4. The normal flora stimulates the development of certain tissues, i. e.. the caecum and certain lymphatic tissues (Peyer’s patches) in the GI tract. The caecum of germ-free animals is enlarged, thin-walled, and fluid- filled, compared to that organ in conventional animals. Also, based on the ability to undergo immunological stimulation, the intestinal lymphatic tissues of germ-free animals are poorly-developed compared to conventional animals. 5. The normal flora stimulates the production of cross-reactive antibodies. Since the normal flora behaves as antigens in an animal, they induce an immunological response, in particular, an antibody-mediated immune (AMI) response. Low levels of antibodies produced against components of the normal flora are known to cross react with certain related pathogens, and thereby prevent infection or invasion. Antibodies produced against antigenic components of the normal flora are sometimes referred to as "natural" antibodies, and such antibodies are lacking in germ-free animals.
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Negative significance of microflora.
- potential pathogens can cause disease - endogenous infections (pyo inflammatory processes, etc.) under the decrease of immunity resistance;
- enteropathogenic E. coli strains cause colienteritis and gastroenteritis in children, and escherichiosis in adults;
- oral microflora is a cause of caries;
- are the sources of drug resistance genes;
- skin microflora is a cause of acne, pyoderma, furunculosis.
What is Dysbiosis?
- Quantitative and qualitative changes in the composition of normal microflora (bacteria and other groups of microbe). There is a loss of normal functions of the microflora.
Dysbiosis is a term for a microbial imbalance that most often affects a person’s digestive tract. That being said, dysbiosis can also affect the skin, eyes, lungs, ears, nose, sinuses, nails, and vagina.
Dysbiosis is also sometimes called dysbacteriosis or bacterial dysbiosis. That is because the gastrointestinal tract (GI tract) contains both “good” and “bad” bacteria to form the gut flora—also called the gut microbe. But, other tiny organisms also reside in the gastrointestinal tract, including yeast, fungus, viruses, and parasites.
The dysbiosis pronunciation is “diss-bi-osis.” Russian-born microbiologist and zoologist, Dr. Elie Metchnikoff, would first coin the term in the 20th century. Dr. Metchnikoff is the first scientist to discover the impact of the properties of probiotics—also known as that “good bacteria.” The terms “dys” and “symbiosis” translate to “not living in harmony.”
When the gut flora is balanced, it is called “orthobiosis,” which again is a term introduced by Dr. Metchnikoff in the early 1900s. He considered dysbiosis so serious that is also said, “death begins in the gut.” The issue here is that not all of the friendly organisms in the gut flora are “friendly.” In fact, when there is an overgrowth of bacteria, parasites, fungus, yeast, or other organisms, it can lead to dysbiosis.
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