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The two faces of E. coli: good bug or bad bug?
Min-Ju Kim and Keun-Sung Kim  |  keunsung@cau.ac.kr
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승인 2012.06.05  09:53:37
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E. coli is a bacterium; a one-celled organism that is too small to see by the naked eye. E. coli is an abbreviation of the organism’s full scientific name: Escherichia coli. Scientists and consumers normally use E. coli for short. E. coli got its first name, Escherichia, from the German pediatrician Theodor Escherich, who discovered the bacteria in1885. Its second name, coli, means “from the colon”, which is the organism’s natural habitat. It is commonly called “dae-jang-gyun” in Korean, literally meaning “colon bacterium”. Most E. coli live and grow harmlessly in the gastrointestinal tract, or gut, of many animals, including humans.
 
   
 
1. How has E. coli contributed to our understanding of biology?
Yet despite all the attention given to their harmful siblings, most E. coli are not harmful to humans, and some are even beneficial. Many of us host a population of E. coli in our gut that aids digestion and protects us from other harmful microbes. Scientists have used strains of E. coli to study fundamental biological processes, contributing to many important scientific breakthroughs and teaching generations of biology students the rudiments of the scientific method. In fact, E. coli wins a record number (eleven times so far!) of Nobel prizes. Other E. coli strains are utilized by researchers in industry to produce important compounds we use every day.
 
2. What is the difference between “good”E. coli and “bad” E. coli?
The big difference between the “good” E. coli strains that inhabit our gut and the “bad” E. coli strains that make us sick is all in their DNA. E. coli is genetically promiscuous. It can exchange genes with other strains of E. coli and even other types of bacteria.
The most common way that E. coli and other bacteria exchange genes is by way of infection with special viruses that target bacteria, called bacteriophages. These special viruses reproduce themselves by injecting their genes into E. coli and other bacteria where the viral genes begin a program that hijacks the bacterium’s internal machinery, effectively taking over the bacterium. Once this happens the hijacked machinery begins to produce more viruses by replicating the virus genes and outer cover, or capsid, of the virus. Once new viruses have been assembled from these parts, they escape and infect other bacteria.
 
   
 
3. How do “bad” E. coli make us sick?
“Bad” E. coli cause illness by disrupting the normal function of the intestines.There are several ways that E. coli can do this with different severities, and different strains of E. coli may possess one or more of these traits. There are many physiological factors involved in whether or not someone is sickened by exposure to “bad” E. coli.
 
4. How does our food become contaminated with E. coli?
It all starts with poop. This may seem frivolous or disgusting, but it is quite accurate. Because E. coli lives in the gut, transmission of E. coli from one organism to another is predominantly from feces to mouth. The source of E. coli in almost all food and water contamination events can be traced back to exposure to fecal matter at some point in the food chain; whether it is on the farm, at the processing plant, in transportation, during retail, at the restaurant, or even during preparation in our homes. At every step of the path from the farm to the table, there are many ways to reduce the likelihood of E. coli from contaminating the food supply, and treating food so that contamination is eliminated before the food reaches the consumer. But the final line of defense, handling and cooking food properly, will remain the responsibility of the cook and consumer.
 
E. coli has accompanied humans and larger animals for millennia. It has become an important part of our gut and, much more recently, a remarkable tool for scientific study. However, there are still “wild” strains that have the capacity to cause illness and death and we should expect new strains to emerge that will continue to threaten our health and the safety of our food. Therefore, we cannot predict how E. coli will impact mankind in the future, but we know that it will always be with us.
 
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