E. Coli: A Model Organism from Theodor Escherich's Legacy
By Dave Gallup, Co-Founder of EMLab P&K
In the late 1800's, the German pediatrician and bacteriologist, Theodor Escherich, was dismayed by the fact that many babies were dying of diarrhea. Because he believed in the "germ theory of disease," he felt that an organism was the causative agent and set about trying to find it. These investigations led him to discover what he called Bacillus communis coli, a Gram negative, rod-shaped bacterium, that is found in the lower intestines of humans as well as other warm-blooded organisms. After his death, it was renamed in his honor as Escherichia coli, commonly referred to and abbreviated as E. coli.1
Escherichia coli has become a "model organism" for studying many of life's essential processes. A model organism is a species that has been widely studied, usually because it is easy to maintain and breed in a laboratory setting and has particular experimental advantages.2 Due to its rapid growth rate, simple nutritional requirements, well established genetics and completed genomic sequence, more is now known about E. coli than any other living organism.3 It is currently the most widely-used organism in molecular genetics4 and many Nobel prizes have been awarded for studies based upon E. coli.1
E. coli has a cell division rate of about once every 30 minutes,5 enabling rapid adaptation to the environment. This rapid division rate has facilitated a long term evolutionary experiment conducted in the lab. Beginning in 1988, Richard Lenski has tracked genetic changes in 12 nearly identical populations of E. coli, reaching 50,000 generations on February 24th of this year.6 Lenski's study is being conducted with a strain of E. coli that reproduces asexually to facilitate a better understanding of random genetic mutations. There are, however, strains of E. coli that reproduce sexually and can transfer DNA from one cell to another.
In 2002, Dr. Alan Parsons and Dr. Richard Heal published test results that demonstrated two physically separated E. coli colonies were capable of conferring resistance to commonly used antibiotics from one colony to the other via an air gap. If this air gap was closed, no resistance was conferred.7
In the environment, E. coli bacteria have been commonly found in recreational waters. Since they are harbored in all warm-blooded animals and generally do not survive long in the outdoors (although they have survived up to 5 years1), they are often used as a marker for the presence of recent fecal contamination. However, E. coli presence does not necessarily indicate human waste. E. coli 0157:H7, for example, is primarily found in dairy and beef cattle. Further, E. coli has been recovered from contaminated fruits, vegetables, water, soil and flies.8
As implied by the opening of this article, some strains of E. coli are capable of causing diarrhea in humans. Other strains of E. coli are a normal part of the bacterial flora in our guts. Babies are born without any E. coli in their digestive tract but become inoculated with it about 40 hours after birth, most frequently from food or their caretakers. This is part of the reason why the excrement of newborns has no smell. Some of these E. coli are beneficial, synthesizing vitamin K, for example.9
Obviously, given the media attention that is occasionally directed towards E. coli, other strains are neither beneficial, nor benign. Most of the diseases caused by these strains are gastrointestinal infections, neonatal meningitis, and urinary tract infections.10 Other illnesses may also be caused by E. coli, but are more rare. Most, but not all illnesses caused by E. coli can be successfully treated with antibiotics, although with its ability to quickly adapt to its environment and the increasingly widespread use of antibiotics, including their use as growth promoters in animal foods, it's unclear how long this will be the case.
The most famous strain of virulent E. coli is O157:H7, which can cause bloody diarrhea and occasionally kidney failure.11 The most common route of infection with O157:H7 is from eating undercooked ground beef, which will look, smell, and taste normal even though it is infected with O157:H7. Other sources of infection include unpasteurized juice, contact with infected animals, raw lettuce, and drinking inadequately treated water.
As far as EMLab P&K's activities with "sick buildings," IAQ, and helping people have a healthy home and business environment, sewage spills, category 3 water (hazardous), and other exposures to contaminated water, can be cause for concern for possible infections from virulent strains of E. coli as well as other pathogenic microorganisms. From a scientific standpoint, it's not clear that sampling in the face of obvious sewage or category 3 water-related incidents adds any value, since the results are unlikely to change how the IICRC S500 Standard would be implemented in these situations. Sampling in the beginning is sometimes necessary for non-scientific reasons, such as when an insurance adjuster needs the data to enable a claim to be processed. Reasons to sample after a clean up include giving the end client peace of mind, confirming the determination that the clean up was successful, and providing the project with the appropriate documentation based on current standard industry practices in the case of future lawsuits. If the sampling is intended to help verify that the clean up/decontamination was performed well, consider taking representative, or random wet swabs of the affected areas, especially areas that are difficult to decontaminate, or major contamination flow pathways, such as corners, under wall sill plates, and/or in grout, if such surfaces were involved. EMLab P&K does not advocate taking air samples for E. coli in most situations, even as part of the clean up, as they are an indirect measure of contamination and usually come up negative. The E. coli analysis EMLab P&K most often recommends in these situations is a presence/absence test for E. coli, or an E. coli sewage screen, rather than a quantitative analysis, because the desired result is to have no E. coli present. Consequently, a presence/absence type of E. coli analysis saves money while also providing exactly the type of information needed.
E. coli is a complex organism. Some strains are beneficial and some clearly harmful. It's possible we may be able to develop strains to do some surprising things. At UCSF, they are trying to engineer E. coli to detect, invade, and release toxins within cancerous tumors.12 If they pull it off, it would be a fabulous development enabled by Theodor Escherich's work over a century ago.
1. Scientific American (podcast): Everything You Ever Wanted to Know about E. Coli (Part 1)
2. Wellcome Trust - The Human Genome: What are 'model organisms'?
3. Microbes in Norwich (MICRON): Escherichia coli
4. Wikipedia: Model organism
5. CyberCell™ Database (CCDB): E. coli Statistics
6. Lenski, R.E. (2010). The E. coli long-term experimental evolution project site.
7. Heal, R.D. & Parsons, A.T. 2002. Novel intercellular communication system in Escherichia coli that confers antibiotic resistance between physically separated populations. J. Appl. Microbiology 92 (6): 1116-1122.
8. Canadian Journal of Animal Science: Transmission and control of Escherichia coli O157:H7 — A review.
9. American Society for Microbiology: Biosynthesis of Vitamin K (Menaquinone) in Bacteria (pdf)
10. Wikipedia: Escherichia coli
11. Wikipedia: O157:H7
12. Scientific American (podcast): Everything You Ever Wanted to Know about E. Coli (Part 2)
This article was originally published on March 2010.