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By: Justin Bosch


Figure 1: Scanning electron micrograph of Escherichia coli (E. coli)

After many years of extensive research we now know that E. coli is a rod-shaped bacterium that is capable of respiring both aerobically and anaerobically depending on the presence of oxygen. This ability is more commonly known as a facultative anaerobe. We also know that it stains Gram-negative due to the bacterium's cell wall and outer membrane obtaining the color from safranin, a red counterstain. The cell wall also protects the bacteria from antibiotics like penicillin [2].

E. coli is not a picky bacterium; they can live on a plethora of substrates and laboratory media due to their ability to deal with anaerobic and aerobic conditions. They also can grow and reproduce at a wide range of temperatures; however, Escherichia coli's optimal temperature for reproduction is around thirty-seven degrees celsius.

Additionally, E. coli is an incredibly diverse species, both genetically and phenotypically. As a matter of fact, amidst all strains of E. coli, only around twenty percent of their genome are mutual or shared. Although most of these unique differences may only be distinguishable at the molecular level, they may have effects on a larger scale; such as, alter the organism's physical makeup. The vast amount of differences in this species allows for it to adapt to its distinct environment possibly; for example, many strains of the bacteria have grown to be host-specific. Some strains also have adapted to be resistant to antimicrobial agents.

Even though there is a considerable amount of total E. coli strains in the world, most strains are known to reside in the intestine of warm-blooded organisms like humans. Most strains are harmless; matter of fact, they are known to aid the health of their host, especially during digestion as a part of a symbiotic relationship. For instance, Escherichia col is known to facilitate and help the health of humans, particularly the health of its immune and digestive systems. E. coli produces certain probiotics that improve our immune responses by providing and stimulating the production of antibodies in the gut to counter a plethora of conditions, like diseases and infections. Therefore, with E. coli protecting the small intestines, our immune system does not need to do so, allowing for it to combat other infections and diseases in other parts of the body.

As we know, this species counteracts many conditions, such as infections in the gut. However, this bacterium does much more to aid intestinal problems. For example, E. coli promotes digestion by creating digestive enzymes that help in breaking down the food in our intestines, allowing for the absorption of the critical nutrients of our food to be facilitated. Therefore, promoting a usual bowel function provides for the discomfort of constipation and infectious diarrhea to be reduced. As well as ridding the gut of the various toxins and waste dwelling in the body, thus, decreasing bloating. All in all, E. col is immensely important to the health of the mammalian digestive system.


Escherichia coli, also known as E. coli, was first observed by Theodor Escherich in 1885. The pediatrician detected the microbe in the feces of his healthy patients; he then named it Bacterium coli commune because it was found in the colon.

Because of the vast amount of medical benefits, E. coli has been a centerpiece of scientific studies since it was first discovered to the present. In 1946 Escherichia coli was used first to detect bacterial conjugation, Edward Tatum and Joshua Lederberg. "Bacterial conjugation is a sexual mode of genetic transfer in the sense that chromosomal material from two sexually distinct types of cells are brought together in a defined and programmed process." [1]. To this day, E. coli remains the primary model for studying bacterial conjugation soon after Seymour Benzer completed experiments to study the gene structure of T4 and E. coli because no one knew whether the genes were using branching patterns or linear structures. Many studies have been performed using E. coli since then. For example, A more recent study was done in 2009 workers were separated into two groups to test medical benefits. The study found that workers that took the E. coli instead of the placebo had a smaller amount of respiratory and digestive issues compared to those that did not.

A plethora of experiments have been done about E. coli, none more prominent in microbial science than that of Richard Lenski. This study began in 1988 and continues to this day in order to observe the evolution of the bacterium and its different populations. This study has produced various findings and data, one being that a particular strain and population of Escherichia coli can digest citrate, a derivative of citric acid.


Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2018, Kenyon College.
1. “Bacterial Conjugation.” Bacterial Conjugation - an Overview | ScienceDirect Topics,

2. National Geographic Society. “Escherichia Coli (E. Coli).” National Geographic Society, 22 May 2019,