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Microbial Flora of the Healthy Human Host, Host-Microbe Interactions- The Process of Infection topics include: Normal flora, human host, normal flora distribution, microbial adherence, epithelial cell layers penetration and microbial virulence factors.
The normal microbial flora of a healthy human host is the population of microorganisms that live on and inside the skin and mucous membranes. This population is also known as the normal microbiota.
The human microbiota includes: Unicellular eukaryotic microbes: Such as fungi and protozoa Prokaryotes: Such as bacteria and archaea Acellular organisms: Such as viruses
The human body contains about 10^13 cells, but it also contains about 10^14 bacteria. This bacterial population is the normal microbial flora. The most common bacteria of the skin flora are the Gram-positive, catalase positive cocci of the genera Staphylococcus and Micrococcus. The intestinal microflora is a complex ecosystem that contains over 400 bacterial species. The flora is sparse in the stomach and upper intestine, but luxuriant in the lower bowel.
Some microbes from normal flora can be opportunistic pathogens. These are microbes, such as fungi and bacteria, that take advantage of a host's weakened immune system. A host-pathogen interaction is how microbes or viruses sustain themselves within host organisms. The term is most commonly used to refer to disease-causing microorganisms.
The host-pathogen interaction depends on the following factors: The host's susceptibility Pathogen virulence factors Route of entry Mode of pathogen transmission A variety of environmental factors
A critical stage in the host-pathogen interaction is the adhesion of the pathogen to the host's surface. A pathogen may be any harmful microbial agent such as a bacterium, virus, protozoa, fungus, or helminth. Humans and animals have “friendly” organisms throughout their bodies that survive as normal flora and colonize a host but do not cause disease.
The body contains two types of normal flora: Host defenses, Microorganisms. A healthy human fetus is sterile until just before birth. It is exposed to microbes during passage through the birth canal. These microbes take up residence, and others from food, humans, and the environment soon also become established on the newborn.
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