Exogenous bacteria

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Exogenous bacteria are microorganisms introduced to closed biological systems from the external world.[1] 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.[2] 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.[3] Exogenous bacteria can be introduced into a closed ecosystem as well, and have mutualistic benefits for both the microbe and the host.[2] A prominent example of this concept is bacterial flora, which consists of exogenous bacteria ingested and endogenously colonized during the early stages of life.[4] 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.[5] Pathogenic exogenous bacteria can enter a host via cutaneous transmission, inhalation, and consumption.[6]

Exogenous vs. Endogenous Bacteria[edit]

Only a minority of bacteria species cause 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.[7] Disease can occur when microbes included in normal bacteria flora enter a sterile area of the body such as the brain or muscle.[7] 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.[7] This causes a urinary tract infection. Infections caused by exogenous bacteria occurs when microbes that are noncommensal enter a host.[7] 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.[7]

Diseases Caused by Exogenous Bacteria[edit]

Waterborne and Foodborne[edit]

Microbial ecosystems in aquatic environments depend on a variety of factors including pH, temperature, and light exposure.[2] Exogenous bacteria supported in specific aquatic environments can enter an host via consumption. Additionally, exogenous bacteria can enter a secondary host through an intermediate host such as insects and parasites.[8] Exogenous bacteria can also enter an enclosed ecosystem via ingestion of contaminated food.Food-borne diseases such as Salmonella poisoning are transmitted by food not properly cooked or by individuals infected with the pathogen.

Salmonella enterocolitis[edit]

One of the most common food-borne illnesses, Salmonella poisoning is caused by ingestion of unsanitary conditions during food preparation.[9] Salmonella can also be transmitted to humans via reptiles like turtles and iguanas, which are known carriers of pathogen.[9] Symptoms include chills, diarrhea[9] and fever.


Cholera is a waterborne infection caused by the bacterium Vibrio chloerae, and is transmitted via food or water that is contaminated with fecal matter.[10] Vibrio chloerae releases a toxin that induces an increased amount of water in the small intestines.[10] Symptoms primarily observed include, watery diarrhea and vomiting that can cause dehydration and death if not treated.[10] An estimated 3-5 million cases of Cholera occur yearly around the world.[11] The exogenous bacteria derived infection is primarilyfound in Africa, Asia, as well as Central and South America.[10]


Campylobacter infections are transmitted to a host via contaminated water and food, sexual activity, and interaction with infected animals.[6] Symptoms include diarrhea, cramping, and abdominal pain.[12] Campylobacter can cause disease in both humans and animals, and most human cases are induced by the species Campylobacter jejuni.[12]

Terrestrial Exogenous Bacteria[edit]

Of all the residential microbes found in soil, bacteria is the smallest and most abundant.[13] According to studies, there is an estimated 60,000 different types of bacteria that reside in the soil.[13] Terrestrial bacteria can characteristically be either aerobic or anaerobic, and some can be pathogenic if consumed by a host.[13]


Anthrax is a disease caused via a bacterium that resides in soil, and predominately affects animals more than humans.[9] Anthrax is also considered a zoonotic disease and is transmitted to humans via contact with an infected animal host.[6] The disease is caused by gram-positive Bacillus anthracis. (B. anthracis) and is found globally.[6] B anthracis can enter a host via cutaneous transmission, inhalation, and/or consumption.[6]


Botulism is a rare disease caused by the bacterium Clostridium botulinum.This microbe is primarily found in the soil or untreated water.[14] Botulism spores can survive in unproperly canned or ill-prepared foods.[14] Even ingesting trace amounts of the spores can lead to severe poisoning that causes symptoms such as vomiting, nausea, and even paralysis.[14]

See also[edit]


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  2. ^ a b c Willey, Sherwood & Woolverton 2011, pp. 673–737.
  3. ^ Willey, Sherwood & Woolverton 2011, pp. 964–72.
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  5. ^ "Exogenous Bacteria." Bacteria Microbes. N.p., n.d. Web. 29 Apr 2012. <http://bacteria.health-tips-diseases.com/2009/02/exogenous-bacteria-and-disease.html>.
  6. ^ a b c d e Willey, Sherwood & Woolverton 2011, pp. 964–5.
  7. ^ a b c d e "Bacteria." ENotes. ENotes.com Inc., 2012. Web. 29 Apr 2012. <http://www.enotes.com/bacteria-reference/bacteria-171754>.
  8. ^ "Mosquitoes and Disease." Prevention and Control. Illinois Department of Public Health, n.d. Web. 28 Apr 2012. <http://www.idph.state.il.us/envhealth/pcmosquitoes.htm>
  9. ^ a b c d MedlinePlus Encyclopedia Salmonella enterocolitis
  10. ^ a b c d "Cholera." PubMed Health. US National Library of Medicine, n.d. Web. 28 Apr 2012. <https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001348/>.
  11. ^ "Cholera." Media Centre. World Health Organization, n.d. Web. 28 Apr 2012. <http://www.who.int/mediacentre/factsheets/fs107/en/index.html>
  12. ^ a b "Campylobacter." National Center for Emerging and Zoonotic Infectious Diseases. Center for disease Control and Prevention, n.d. Web. 28 Apr 2012. <https://www.cdc.gov/nczved/divisions/dfbmd/diseases/campylobacter/>.
  13. ^ a b c "Soil Bacteria." Soil Biology Basics. n. page. Web. 28 Apr. 2012.<http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0017/41642/Soil_bacteria.pdf>.
  14. ^ a b c "Botulism." PubMed Health. US National Library of Medicine, n.d. Web. 29 Apr 2012. <https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001624/>.


  • Willey, Joanne; Sherwood, Linda; Woolverton, Christopher (2011). Prescott's Microbiology (8th ed.). New York: McGraw Hill. ISBN 978-0-07-337526-7.