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Exogenous bacteria
Exogenous bacteria are microorganisms introduced to closed biological systems from the external world. They exist in aquatic and terrestrial environments, as well as the atmosphere. Microorganisms in the external environment have existed on Earth for 3.5 billion years. Exogenous bacteria can be either benign or pathogenic. Pathogenic exogenous bacteria can enter a closed biological system and cause disease such as ''Cholera,'' which is induced by a waterborne microbe that infects the human intestine. Exogenous bacteria can be introduced into a closed ecosystem as well, and have mutualistic benefits for both the microbe and the host. A prominent example of this concept is ''bacterial flora,'' which consists of exogenous bacteria ingested and endogenously colonized during the early stages of life. Bacteria that are part of normal internal ecosystems, also known as bacterial flora, are called ''Endogenous Bacteria''. A significant amount of prominent diseases are induced by ''exogenous bacteria'' such as ''gonorrhea'', ''meningitis'', ''tetanus'', and ''syphilis.''〔"Exogenous Bacteria." Bacteria Microbes. N.p., n.d. Web. 29 Apr 2012. .〕 Pathogenic exogenous bacteria can enter a host via cutaneous transmission, inhalation, and consumption.
== Exogenous vs. Endogenous Bacteria==
A small fragment of bacteria causes disease in humans, and many species colonize in the human body to create an ecosystem known as bacterial flora. Bacterial flora is endogenous bacteria, which is defined as bacteria that naturally reside in a closed system.〔"Bacteria." ENotes. ENotes.com Inc., 2012. Web. 29 Apr 2012. .〕 Disease can occur when microbes included in normal bacteria flora enter a sterile area of the body such as the brain or muscle.〔 This is considered an endogenous infection. A prime example of this is when the residential bacterium E. coli of the GI tract enters the urinary tract.〔 This causes a urinary tract infection. Infections caused by exogenous bacteria occurs when microbes that are noncommensal enter a host.〔 These microbes can enter a host via inhalation of aerosolized bacteria, ingestion of contaminated or ill-prepared foods, sexual activity, or the direct contact of a wound with the bacteria.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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