A diverse microbial flora is found in the oral cavity, and streptococcal anaerobes inhabit the split gums. The pharynx may be an entry point and first colonization for Neisseria, Bordetella, Corynebacterium and Streptococcus spp. Many elements of the normal flora can act as opportunistic pathogens, especially in hosts prone to rheumatic heart disease, immunosuppression, radiotherapy, chemotherapy, perforated mucous membranes, etc. The flora of split gums causes tooth decay in about 80% of the population. In 2008, the National Institutes of Health launched the Human Microbiome Project, which aims to help understand the effects of human bacterial flora on health. [6] Biologists believe that bacterial flora may play a role in diseases such as multiple sclerosis. In addition, the study of flora can have industrial benefits such as supplements such as probiotics. The live microorganisms in probiotics are believed to have health benefits and have been used in studies on gastrointestinal diseases and allergies. The number of bacteria on an individual`s skin remains relatively constant; The survival of the bacterium and the extent of colonization probably depend partly on the exposure of the skin to a particular environment and partly on the innate and species-specific bactericidal activity of the skin species. In addition, a high degree of specificity is involved in the adhesion of bacteria to epithelial surfaces. Not all bacteria adhere to the skin; Staphylococci, which are the main component of the nasal flora, have a clear advantage over viridan streptococci in the colonization of the nasal mucosa. Conversely, viridian streptococci are not observed in large numbers on the skin or nose, but dominate the oral flora. Clinical conditions that can be caused by members of normal flora.
Although the above suggests that bacterial flora may be undesirable, studies on animals treated with antibiotics suggest that the flora protects individuals from pathogens. The researchers used streptomycin to reduce normal flora and then infected the animals with streptomycin-resistant salmonella. Normally, about 106 organisms are needed to establish gastrointestinal infection, but in streptomycin-treated animals with altered flora, fewer than 10 organisms were needed to cause infectious diseases. Other studies have suggested that fermentation products (acetic acid and butyric) produced by normal flora inhibit the growth of salmonella in the gastrointestinal tract. Figure 6-2 shows some of the factors that are important in the competition between normal flora and pathogenic bacteria. This chapter briefly described normal human flora; However, the pathogenic mechanisms of the different genera or the clinical syndromes in which they are involved have not been discussed. Although such material is presented in other chapters, note that rupture of mucous surfaces often leads to infection of the host by members of the normal flora. Caries, periodontitis, abscesses, foul-smelling excretions and endocarditis are features of infections with members of the normal human flora (Fig. 6-4). In addition, a host deficiency (e.g. in patients with heart failure or leukemia) or host defense (due to immunosuppression, chemotherapy or radiotherapy) prevent normal flora from suppressing transient pathogens or members of normal flora themselves to invade the host.
In both cases, the host may die. There is more information about the animal than about the human microflora. Animal studies have shown that unusual filamentous microorganisms attach to ileal epithelial cells and alter host membranes with little or no adverse effects. Microorganisms were observed in thick layers on gastrointestinal surfaces (Fig. 6-3) and in the crypts of Lieberkuhn. Other studies suggest that the immune response may be modulated by the intestinal flora. Studies on the role of gut flora in the biosynthesis of vitamin K and other host-usable products, the conversion of bile acids (possibly into cocarcinogens) and the production of ammonia (which may play a role in hepatic coma) show the dual role of microbial flora in influencing host health. Further fundamental studies of the human intestinal flora are needed to define its effect on humans. The terms «flora» and «fauna» were first used by Carl Linnaeus of Sweden in the title of his 1745 work[1] Flora Suecica et Fauna Suecica. At that time, biology focused on macro-organisms. Later, with the advent of microscopy, newly discovered ubiquitous microorganisms were integrated into this system. Next, fauna included mobile organisms (animals and protists as «microfauna») and flora as seemingly motionless organisms (plants/fungi; and bacteria as «microflora»).
The terms «microfauna» and «microflora» are common in ancient books, but they have recently been replaced by the more appropriate term «microbiota». [2] The microbiota includes archaea, bacteria, fungi and protists. S. epidermidis is a major inhabitant of the skin, accounting for more than 90 percent of the resident aerobic flora in some areas. Mineralization and release of nutrients from consumed microbial biomass The population of microorganisms that live on healthy, normal skin and mucous membranes is called their normal microbial flora. There are two categories of microorganisms that are constantly present in the skin and mucous membranes: Although normal flora can inhibit pathogens, many of their limbs can cause diseases in humans. Anaerobes in the intestinal tract are the main agents of intra-abdominal abscesses and peritonitis. Intestinal perforations caused by appendicitis, cancer, heart attack, surgery or gunshot wounds almost always sow the abdominal cavity and adjacent organs with normal flora. Anaerobes can also cause problems in the gastrointestinal lumen. Treatment with antibiotics can predominate certain anaerobic species and cause disease. For example, Clostridium difficile, which may remain viable in a patient on antimicrobial therapy, can cause pseudomembranous colitis.
Other intestinal pathological conditions or surgeries can cause bacterial overgrowth in the upper part of the small intestine. Anaerobic bacteria can then deconjugate bile acids in this region and bind existing vitamin B12 so that the vitamin and fats are poorly absorbed. In these situations, the patient was usually compromised in some way; Therefore, infection caused by normal intestinal microflora is secondary to another problem. The benthic microflora of marine sands includes bacteria, blue-green bacteria (cyanobacteria), autotrophic flagellates and diatoms. Those attached to grains of sand are commonly called epipsamon (Fig. 4.1). During strong wave movement, living diatoms can be mixed at considerable depths in sediments, while in more sheltered conditions or in the sublivodal zone, they tend to concentrate towards the surface. The photic zone in the sand deepens with increasing particle size, but usually does not exceed 5 mm in thickness; in addition, longer wavelengths penetrate deeper, as the refractive index of the quartz increases with decreasing wavelength (Fig. 4.2). The total surface area of the sand grains increases with decreasing particle size (Fig. 4.3), which provides more space for fixation by microflora, but reduces the pore space. In sediments that are not well supplied with oxygen, various components (algae, photosynthetic bacteria, flagellates, etc.) can form layers at different depths in the sand.
However, this is less pronounced in exposed situations. Vaginal flora changes with the individual`s age, vaginal pH and hormone levels. Transient organisms (e.g., Candida spp.) often cause vaginitis. The distal urethra contains a sparse mixed flora; These organisms are present in urine samples (104/ml) unless a clean sample is obtained in the middle of the river.