This multi-million dollar industry is aimed at microbial genocide, and it is only the hopelessness of their task, which guarantees the survival of our species. Stanley Falkow, an infectious disease specialist from Stanford University, put it this way:.
For most commensal bacterial species, their replication on or within us is essential to their survival. Moreover, our own survival is likely dependent on the presence of those microorganisms. ASM News Some sites are normally colonized by several hundred different types of microorganisms.
If temporarily disturbed for example, by washing the skin or using antibiotics , the resident flora usually promptly reestablishes itself. Rather than causing disease, the resident flora often protects the body against disease-causing organisms.
Such conditions include. A weakened immune system as occurs in people with AIDS or cancer, people taking corticosteroids, and those receiving cancer chemotherapy. When antibiotics used to treat an infection kill a large proportion of certain types of bacteria of the resident flora, other resident bacteria or fungi can grow unchecked.
For example, if women take antibiotics for a bladder infection, the antibiotics kill some of the resident flora, allowing yeast in the vagina to multiply and cause a vaginal yeast infection. Injury or sometimes surgery can allow resident flora to enter areas that are not supposed to have bacteria and cause infection. For example, a cut on the skin can allow resident skin flora to cause an infection under the skin.
Surgery on the large intestine sometimes allows the resident flora in the intestine to spill into sterile areas in the abdomen and cause very serious infection.
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Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume 7. Article Contents Abstract. Baylor College of Medicine. Oxford Academic. Normal Flora of the 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 composed solely of the soft tissues of the lips, cheeks, tongue and palate, which are kept moist by the secretions of the salivary glands.
At birth the oral cavity is sterile but rapidly becomes colonized from the environment, particularly from the mother in the first feeding. The eruption of the teeth during the first year leads to colonization by S. These bacteria require a nondesquamating 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 and spirochetes colonize around puberty.
Figure 6. Various streptococci in a biofilm in the oral cavity. The normal bacterial flora of the oral cavity clearly benefit from their host who provides nutrients and habitat. There may be benefits, as well, to the host. The normal flora occupy available colonization sites which makes it more difficult for other microorganisms nonindigenous species to become established. Also, the oral flora contribute 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 substances such as fatty acids, peroxides and bacteriocins.
On the other hand, the oral flora are the usual cause of various oral diseases in humans, including abscesses, dental caries, gingivitis, and periodontal disease. If oral bacteria can gain entrance into deeper tissues, they may cause abscesses of alveolar bone, lung, brain, or the extremities.
Such infections usually contain mixtures of bacteria with Bacteroides melaninogenicus often playing a dominant role. If oral streptococci are introduced into wounds created by dental manipulation or treatment, they may adhere to heart valves and initiate subacute bacterial endocarditis.
Figure 7. Colonies of E. Normal Flora of the Gastrointestinal Tract The bacterial flora of the gastrointestinal 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 GI 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, at least half the population in the United States is colonized by a pathogenic bacterium, Helicobacter pylori. Since the s, this bacterium has been known to be the cause of gastric ulcers, and it is probably a cause of gastric and duodenal cancer as well.
The Australian microbiologist, Barry Marshall, received the Nobel Prize in Physiology and Medicine in , for demonstrating the relationship between Helicobacter and gastric ulcers. Figure 8. Helicobacter pylori. The proximal small intestine has a relatively sparse Gram-positive flora, consisting mainly of lactobacilli and Enterococcus faecalis.
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