Thursday, March 17, 2011

Mutualism Between Humans and E.coli


Escherichia coli, commonly referred to as E.coli, is a rod-shaped bacterial germ that is found in the intestinal tract of humans and other warm-blooded animals. Although some strains of E.coli, such as E.coli O157:H7, can cause food poisoning and serious illnesses such as Hemolytic Uremic Syndrome, most strains are harmless and are part of the normal flora in the gut, providing beneficial Vitamin K to their hosts. [2]
E.coli's natural habitat is the gut of warm-blooded animals; however, they can survive outside host bodies in environments such as water or mud that are contaminated with fecal wastes. Due to its residence in warm-blooded animals, E.coli's global distribution spans throughout most continents in the world; however, the free-living species prefer warm places rather than cooler places.[3]
Fetuses of animals lack bacteria; however, immediately after birth newborns acquire various kinds of bacteria, including E.coli, through food or water or individuals handling the child. the bacteria travel to the bowels, where it attaches to the mucus of the large intestines and continues to grow.[4] The actual life cycle of E.coli includes both sexual and asexual reproductions. Asexual reproduction occurs through binary fission, while its sexual reproduction is achieved by conjugation between genetically differentiated strains. In mating E.coli, those with F+ or Hfr sex factors are male and those with the F- sex factor is female. A male and female collide by chance and the male transfers its sex factor to the female, completing conjugation. The male and female cells separate and the F- female becomes a partial diploid merozygote. The F- female cell then reproduces by cell division and returns to its monoploid state. Through theses to types of reproduction, E. coli are able to accumulate in the intestines of warm-blooded animals. [5]

Although this blog focuses on E.coli's relationship with humans, as previously stated, E. coli are also found to have similar relationships with other warm-blooded mammals and birds. As stated above, E.coli provide humans with vitamins, such as Vitamin K and B, that are necessary for development and healthy immune systems. [4] In our readings of The Art of Being a Parasite and Parasite Rex, and our class discussions, we know a that mutualistic relationship occurs when both organism are benefiting from the relationship. This relationship between E.coli and humans is mutualistic because while E.coli provide humans with necessary vitamins, humans provide a stable environment for E.coli to live, where they can feed off of the pathogens that come into the intestines.[3]

While there are some pathogenic E.coli strains, most of the strains that reside with humans are harmless. So, though we may come into contact with the pathogenic strains and become ill, the benefit of maintaining the bacteria within our intestines far outweighs the cost of getting sick from the pathogenic strains. Also, without E.coli residing in our intestines, we could not obtain the vitamins that are vital to our development and immune system functionality. Without these vitamins we would become ill anyways, so taking the chance of becoming infected with pathogenic E.coli, which can be cured with antibiotics, is far better than getting rid of beneficial E.coli that helps us dispose of harmful pathogens.

Although, E.coli can survive outside of their host, they cannot get the vast supply of nutrients or the safe environment that their host provides. The bacteria do face the risk of being identified as a pathogen and subsequently being destroyed by the immune system, but outside of the host it faces a environment that has a limited food supply and an unstable climate that would cause the bacteria to die, such as limited water supply.

Humans do not have strategies to encounter E.coli, however E.coli resides in reservoirs, such as water and food that people often drink and eat, so that they can easily be ingested and migrate to the intestines, consuming other pathogens that humans come in contact with and producing vitamins that benefit its host so that the E.coli can continue to have a stable environment.

[1]Joshi, Mohit. "Here's how E.coli bacterium causes illness." (2011) 16 March 2011. Web
[2] "Escherichia Coli."Wikipedia. 16 March 2011.Web
[3] "Escherichia Coli." MicrobeWiki. 16 March 2011. Web
[4] Brown, John C. "What the Heck is an E.coli?" Don't Touch That Doorknob: How Germs Can Zap You and How You Can Zap Back. New York: Warner Books, 2001. Web
[5] "Life Cycle of Escherichia coli." 17 March 2011. Web


  1. I know in mutualistic relationships both parties benefit, but are there any possible costs for E. coli in its relationship with humans?

  2. Vitamin K and B can be acquired through others means, such as taking supplements. With that being said, do you believe that this relationship is truly mutualistic since humans can survive without E. coli and since E. coli can survive outside the human body?

    1. e. coli is our main source of it, its not that they just supply it to us, they make it possible to absorb it, humans can't live without e. coli and yes e. coli. can live outside of the human body but they live longer and reproduce better within us

  3. Morgan- Although most E.coli is harmless, if the pathogenic strain enters into the body with the harmless strain, it could cause an immune response that would destroy all strains of E.coli entering into the body. That is one cost, another cost could be the energy it would cost to enter a warm-blooded animal.

    Prerana- Yes, i still think the relationship is mutualistic because humans cannot actually live without E.coli. I only gave the vitamin example, but e.coli also gets rid of other harmful bacteria that enters the body, so without E.coli humans would be more susceptible to bacterial and viral infections. E.coli can live outside the bodies of humans and other animals, but not permanently due to environmental changes such as purification of their water source.