Exogenous bacteria are microorganisms introduced to closed biological systems from the external world.[citation needed] 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.[1] 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.[2] Exogenous bacteria can be introduced into a closed ecosystem as well, and have mutualistic benefits for both the microbe and the host.[1] A prominent example of this concept is bacterial flora, which consists of exogenous bacteria ingested and endogenously colonized during the early stages of life.[3] 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.[4] Pathogenic exogenous bacteria can enter a host via cutaneous transmission, inhalation, and consumption.[5]
Only a minority of bacteria species cause disease in humans; and many species colonize in the human body to create an ecosystem known as microbiota. Bacterial flora is endogenous bacteria, which is defined as bacteria that naturally reside in a closed system.[6] Disease can occur when microbes included in normal bacteria flora enter a sterile area of the body such as the brain or muscle.[6] 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.[6] This causes a urinary tract infection. Infections caused by exogenous bacteria occurs when microbes that are noncommensal enter a host.[6] 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.[6]
Microbial ecosystems in aquatic environments depend on a variety of factors including pH, temperature, and light exposure.[1] 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.[7] 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.
One of the most common food-borne illnesses, Salmonella poisoning is caused by ingestion of unsanitary conditions during food preparation.[8] Salmonella can also be transmitted to humans via reptiles like turtles and iguanas, which are known carriers of pathogen.[8] Symptoms include chills, diarrhea[8] and fever.
Cholera is a waterborne infection caused by the bacterium Vibrio cholerae, and is transmitted via food or water that is contaminated with fecal matter.[9] Vibrio cholerae releases a toxin that induces an increased amount of water in the small intestines.[9] Symptoms primarily observed include, watery diarrhea and vomiting that can cause dehydration and death if not treated.[9] An estimated 3-5 million cases of Cholera occur yearly around the world.[10] The exogenous bacteria derived infection is primarilyfound in Africa, Asia, as well as Central and South America.[9]
Campylobacter infections are transmitted to a host via contaminated water and food, sexual activity, and interaction with infected animals.[5] Symptoms include diarrhea, cramping, and abdominal pain.[11] Campylobacter can cause disease in both humans and animals, and most human cases are induced by the species Campylobacter jejuni.[11]
Of all the residential microbes found in soil, bacteria is the smallest and most abundant.[12] According to studies, there is an estimated 60,000 different types of bacteria that reside in the soil.[12] Terrestrial bacteria can characteristically be either aerobic or anaerobic, and some can be pathogenic if consumed by a host.[12]
Anthrax is a disease caused via a bacterium that resides in soil, and predominately affects animals more than humans.[8] Anthrax is also considered a zoonotic disease and is transmitted to humans via contact with an infected animal host.[5] The disease is caused by gram-positive Bacillus anthracis. (B. anthracis) and is found globally.[5] B anthracis can enter a host via cutaneous transmission, inhalation, and/or consumption.[5]
Botulism is a rare disease caused by the bacterium Clostridium botulinum. This microbe is primarily found in the soil or untreated water.[13] Botulism spores can survive in unproperly canned or ill-prepared foods.[13] Even ingesting trace amounts of the spores can lead to severe poisoning that causes symptoms such as vomiting, nausea, and even paralysis.[13]