Escherichia coli (IPA: [ˌɛ.ʃəˈɹɪ.kjə ˈkʰoʊ.laɪ]) (E. coli), is one of many species of
bacteria living in the lower intestines of mammals, known as gut flora. When located in the large intestine, it assists
with waste processing, vitamin K production, and food absorption. Discovered in 1885 by
Theodor Escherich, a German pediatrician and
bacteriologist,[1] E. coli are
abundant: the number of individual E. coli bacteria in the feces that a human
defecates in one day averages between 100 billion and 10 trillion.[citation needed] However, the bacteria are not
confined to this environment, and specimens have also been located, for example, on the edge of hot
springs. The E. coli strain O157:H7 is one of hundreds of strains
of the bacterium that causes illness in humans.[2]
E. coli are unable to sporulate. Thus, treatments which kill all active bacteria,
such as pasteurization or simple boiling, are effective for their eradication, without
requiring the more rigorous sterilization which also deactivates
spores.
As a result of their adaptation to mammalian intestines, E. coli grow best in
vivo or at the higher temperatures characteristic of such an environment, rather than the cooler temperatures found in
soil and other environments.
Role in disease
E. coli can generally cause several intestinal and extra-intestinal infections such as urinary tract infections, meningitis, peritonitis, mastitis, septicemia and
Gram-negative pneumonia.
Virulence properties
The enteric E. coli are divided on the basis of virulence properties into enterotoxigenic (ETEC, causative agent of
diarrhea in humans, pigs, sheep, goats, cattle, dogs, and horses), enteropathogenic (EPEC, causative agent of diarrhea in humans,
rabbits, dogs, cats and horses); enteroinvasive (EIEC, found only in humans), verotoxigenic (VTEC, found in pigs, cattle, dogs
and cats); enterohaemorrhagic (EHEC, found in humans, cattle, and goats, attacking porcine strains that colonize the gut in a
manner similar to human EPEC strains) and enteroaggregative E. coli (EAggEC, found only in humans).
Urinary tract infections
It is much more common in females due to the shorter urethra (25–50 mm / 1-2 inches) compared to males (about 20 cm
/ 8 inches). Among the elderly UTI is in roughly equal proportions in men and women. Since bacteria invariably enter the urinary
tract through the urethra (an ascending infection), poor toilet habits can predispose to
infection (doctors often advise women to "wipe front to back, not back to front") but other factors are also important:
(pregnancy in women, prostate enlargement in men) and in
many cases the initiating event is unclear. While ascending infections are generally the rule for lower urinary tract infections
and cystitis, the same may not necessarily be true for upper urinary tract infections like
pyelonephritis which may be hematogenous in origin. Most cases of lower urinary tract
infections in females are benign and do not need exhaustive laboratory work-ups. However, UTI in young infants must receive some
imaging study, typically a retrograde urethrogram, to ascertain the presence/absence of
congenital urinary tract anomalies. Males too must be investigated further. Specific methods of investigation include
x-ray, MRI and CAT scan technology.
Gastrointestinal
Low-temperature electron micrograph of a cluster of
E. coli bacteria, magnified 10,000 times. Each individual bacterium is
oblong shaped.
If E. coli bacteria escape the intestinal tract through a perforation (hole or tear, for example from an
ulcer, a ruptured appendix, or a surgical error) and enter the abdomen, they usually cause peritonitis
that can be fatal without prompt treatment. However, E. coli are extremely sensitive to such antibiotics as streptomycin or gentamycin, so treatment with antibiotics is usually effective. This could rapidly change, since, as noted
below, E. coli rapidly acquires drug resistance.[3]
Certain strains of E. coli, such as Escherichia coli O157:H7,
Escherichia coli O121 and Escherichia coli O104:H21, are toxigenic (some produce a toxin very similar to that seen
in dysentery). They can cause food poisoning
usually associated with eating unwashed vegetables and contaminated meat (contaminated during or shortly after slaughter or
during storage or display). O157:H7 is further notorious for causing serious, even life threatening complications like HUS
(Hemolytic Uremic Syndrome). The usual countermeasure is cooking suspect meat
until it reaches an internal temperature of 160 degrees Fahrenheit (70 °C), or is "well done"; the alternative of careful
inspection of slaughtering and butchering methods (to make sure that the animal's colon is removed and not punctured) has
apparently not been systematically tried. This particular strain is linked to the 2006 United States E. coli outbreak of fresh spinach. Severity of the illness
varies considerably; it can be fatal, particularly to young children, the elderly or the immunocompromised, but is more often
mild. E. coli can harbor both heat-stable and heat-labile enterotoxins. The latter, termed LT, is highly similar in
structure and function to Cholera toxin. It contains one 'A' subunit and five 'B' subunits
arranged into one holotoxin. The B subunits assist in adherence and entry of the toxin into host intestinal cells, where the A
subunit is cleaved and prevents cells from absorbing water, causing diarrhea. LT is secreted by
the Type 2 secretion pathway[4]
It has also been shown that Shiga toxin-producing E. coli (STEC), specifically O157:H7, can be found in filth flies on cattle
farms, in house flies, can grow on wounded fruit and be transmitted to and by fruit flies.[5][6][7]
Since entrotoxigenic coli can be resident in animals which are resistant to the toxin,
they may be spread through direct contact on farms, at petting zoos, etc. They may also be
spread via airborne particles in such environments.[8] The
United States government Department of Agriculture asked in 1978 what the effect of overfeeding animals antibiotics would be. The
American Academy of Science eventually responded that antibiotic resistant E. coli would develop and would be untreatable.
Nonetheless, heavy dosing of antibiotics in swine and cattle feed is a routine practice at large farms.
E. coli is a frequent member of multispecies biofilms. Some strains are piliated and
capable of accepting and transferring plasmids (rings of DNA) from and to other bacteria of the same and different species. E.
coli often carry multidrug resistant plasmids and under stress readily transfer those plasmids to other species. Thus E.
coli and the other enteroccia are important reservoirs of transferable antibiotic resistance.[9]
E. coli possess specific nucleation-precipitation machinery to produce soluble amyloid oligomers and precipitate them as curli, a network
of fibers which bind the bacteria to host cells and each other. The importance of E. coli as a source of amyloid is
unknown, but amyloid fibers are a component of numerous human disease processes including Alzheimer's.[10]
Antibiotic therapy
Appropriate treatment depends on the disease and should be guided by laboratory analysis of the antibiotic sensitivities of
the infecting strain of E. coli. As Gram-negative organisms, E. coli are resistant to many antibiotics that are
effective against Gram-positive organisms. Antibiotics which may be used to treat E.
coli infection include (but are not limited to) amoxicillin as well as other
semi-synthetic penicillins, many cephalosporins, carbapenems, aztreonam, trimethoprim-sulfamethoxazole, ciprofloxacin, nitrofurantoin and the aminoglycosides. Not all antibiotics are
suitable for every disease caused by E. coli, a sensitivity test along with the advice of a physician should be
sought.
Antibiotic resistance is a growing problem. Some of this is due to overuse of
antibiotics in humans, but some of it is probably due to the use of antibiotics as growth promoters in food of animals.[11] Resistance to beta-lactam antibiotics
has become more serious in recent decades as strains producing extended-spectrum beta-lactamases render many, if not all, of the
penicillins and cephalosporins ineffective as therapy. Susceptibility testing should guide treatment in all infections in which
the organism can be isolated for culture.
A study published in the journal Science in August 2007 found that the rate of
adaptative mutations in E. coli is "on the order of 10–5 per genome per generation, which is 1,000 times as high as previous estimates", a finding which may have significance
for the study and management of bacterial antibiotic resistance.[12]
Phage therapy
Phage therapy—viruses that specifically target pathogenic bacteria—has been developed
over the last 80 years, primarily in the former Soviet Union, where it was used to prevent
diarrhea caused by E. coli, among other things, in the Red Army, and was widely
available over the counter. [1] Presently, phage therapy for humans is available only at the Phage Therapy Center in the Republic of Georgia [2] or in Poland.[3]
However on January the 2nd, 2007 the FDA gave Omnilytics approval to apply its 0157:H7 killing phage in a mist, spray or wash
on live animals that will be slaughtered for human consumption. [4]
Vaccine
E. coli vaccines have been under development for many years.[13] In March of 2006, a vaccine eliciting an immune response against the E. coli O157:H7 O-specific polysaccharide conjugated to recombinant exotoxin A of Pseudomonas aeruginosa
(O157-rEPA) was reported to be safe and immunogenic in children two to five years old. It has already been proven safe and
immunogenic in adults.[14] A
phase III clinical trial to verify the large-scale efficacy of the treatment is planned.[14]
In January 2007 the Canadian bio-pharmaceutical company Bioniche announced it has developed a cattle vaccine which reduces the
number of bacteria shed in manure by a factor of 1000, to about 1000 bacteria per gram of manure.[15][16][17]
Strains
Model of successive binary fission in
E. coli
A "strain" of E. coli is a group with some particular characteristics that make it distinguishable from other E.
coli strains. These differences are often detectable only on the molecular level; however, they may result in changes to the
physiology or lifecycle of the bacterium, for example leading to pathogenicity. Different
strains of E. coli live in different kinds of animals, so it is possible to tell whether fecal material in water came from
humans or from birds, for example. New strains of E. coli arise all the time from the natural biological process of
mutation, and some of those strains have characteristics that can be harmful to a host animal.
Although in most healthy adult humans such a strain would probably cause no more than a bout of diarrhea, and might produce no symptoms at all, in young children, people who are or have recently been sick,
or in people taking certain medications, an unfamiliar strain can cause serious illness and even death. A particularly virulent
example of such a strain of E. coli is E. coli O157:H7.
In addition, E. coli and related bacteria possess the ability to transfer DNA via
bacterial conjugation, which allows a new mutation to spread through an existing
population. It is believed that this process led to the spread of toxin synthesis from Shigella to E. coli O157:H7.
ESBL producing E.Coli
Extended-Spectrum Beta-Lactamase (ESBL)–producing E. coli are
antibiotic-resistant strains of E. coli. ESBL-producing strains are bacteria that produce an enzyme called extended-spectrum beta lactamase, which makes them more resistant to antibiotics and makes the
infections harder to treat. In many instances, only two oral antibiotics and a very limited group of intravenous antibiotics
remain effective.
There is increased concern about the prevalence of this form of "superbug" in
the United Kingdom has led to calls for further monitoring and a UK-wide strategy to deal
with infections and the deaths caused[18].
Role in microbiology
Because of its ubiquity, E. coli is frequently studied in microbiology and is the
current "workhorse" in molecular biology. Its structure is clear, and it makes for an
excellent target for novice, intermediate, and advanced students of the life sciences. The strains used in the laboratory have
adapted themselves effectively to that environment, and are no longer as well adapted to life in the mammalian intestines as the
wild type; a major adaptation is the loss of the large quantities of external biofilm mucopolysaccharide produced by the wild type in order to
protect itself from antibodies and other chemical attacks, but which require a large
expenditure of the organism's energy and material resources. This can be seen when culturing the organisms on agar plates; while the laboratory strains produce well defined individual colonies, with the wild type strains the colonies are embedded within this large mass of
mucopolysaccharide, making it difficult to isolate individual colonies.
Bacterial conjugation was first discovered in E. coli, and it remains
the primary model to study conjugation.
Because of this long history of laboratory culture and manipulation, E. coli plays an important role in modern
biological engineering. Researchers can alter the bacteria to serve as "factories" to
synthesize DNA and/or proteins, which can then be produced in large
quantities using the industrial fermentation processes. One of the first useful
applications of recombinant DNA technology was the manipulation of E. coli to
produce human insulin for patients with diabetes.
[5]
Role in water purification and sewage treatment
All the different kinds of fecal coli bacteria, and all the very similar bacteria that live in the ground (in soil or
decaying plants, of which the most common is Enterobacter aerogenes), are grouped
together under the name coliform bacteria. Technically, the "coliform group" is
defined to be all the aerobic and facultative anaerobic, non-spore-forming, Gram-negative, rod-shaped bacteria that ferment lactose with the
production of gas within 48 hours at 35 °C (95 °F). In the body, this gas is released as flatulence. E. coli cells are elongated, 1–2 µm in length and
0.1–0.5 µm in diameter.
The presence of coliform bacteria in surface water is a common indicator of
fecal contamination. E. coli is commonly used as a model organism for bacteria in general. This is usually done using the MPN (most probable number) tests.
This is usually a probabilistic test which assumes bacteria meeting certain growth and biochemical criteria as E. coli and
quantitates it by various methods. "Presence" of E. coli numbers beyond a certain cut-off indicates fecal contamination of water
and indicates further investigation into the matter. Often, a "confirmatory" test - the Eijckman test is done which tests for
growth at a particular temperature. Many of these tests are routinely done at water storage and distribution systems. At other
places, more advanced tests have replaced them. Other organisms like Streptococcus
bovis and certain clostridia species are also used as an index of fecal contamination
of drinking water sources - usually animal in origin. One of the root words of the family's scientific name, "enteric", refers to
the intestine, and is often used synonymously with "fecal". In the field of water
purification and sewage treatment, E. coli was chosen very early in the
development of the technology as an "indicator" of the pollution level of water, meaning the amount of human fecal matter in it,
measured using the Coliform Index. E. coli is used for detection because there are
a lot more coliforms in human feces than there are pathogens (Salmonella typhi is an example of such a pathogen, causing typhoid fever), and E. coli is usually harmless, so it can't "get loose" in the lab and hurt
anyone. However, sometimes it can be misleading to use E. coli alone as an indicator of human fecal contamination because
there are other environments in which E. coli grows well, such as paper mills.
See also
References
- ^ Feng P, Weagant S, Grant, M (2002-09-01). Enumeration of Escherichia coli and the
Coliform Bacteria. Bacteriological Analytical Manual (8th ed.). FDA/Center for Food Safety & Applied Nutrition.
Retrieved on 2007-01-25.
- ^ Escherichia coli
O157:H7. CDC Division of Bacterial and Mycotic Diseases. Retrieved on 2007-01-25.
- ^ Gene Sequence Of Deadly E.
Coli Reveals Surprisingly Dynamic Genome. Science Daily (2001-01-25). Retrieved on 2007-02-08.
- ^ Tauschek M, Gorrell R, Robins-Browne RM,.
"Identification of a protein
secretory pathway for the secretion of heat-labile enterotoxin by an enterotoxigenic strain of Escherichia coli". PNAS
99: 7066-7071.
- ^ Szalanski A, Owens C, McKay T, Steelman C
(2004). "Detection of Campylobacter and Escherichia coli O157:H7 from filth flies by polymerase chain reaction". Med Vet
Entomol 18 (3): 241-6. PMID 15347391.
- ^ Sela S, Nestel D, Pinto R, Nemny-Lavy E,
Bar-Joseph M (2005). "Mediterranean fruit fly as a potential vector of bacterial pathogens". Appl Environ Microbiol
71 (7): 4052-6. PMID 16000820.
- ^ Alam M, Zurek L (2004). "Association of
Escherichia coli O157:H7 with houseflies on a cattle farm". Appl Environ Microbiol 70 (12): 7578-80. PMID
15574966.
- ^ Christie, Tim. "Tests suggest E. coli spread through
air", The Register-Guard, 2002-09-24. Retrieved on [[2007-01-05]].
- ^ Franiczek R, Dolna I, Krzyzanowska B,
Szufnarowski K, Kowalska-Krochmal B, Zielińska M (2006). "[Conjugative transfer frequency of resistance genes from ESBL-producing
Enterobacteriaceae strains isolated from patients hospitalized in pediatric wards]" (in Polish). Medycyna doświadczalna i
mikrobiologia 58 (1): 41-51. PMID 16871972.
- ^ Chapman M, Robinson L, Pinkner J, Roth R,
Heuser J, Hammar M, Normark S, Hultgren S (2002). "Role of Escherichia coli curli operons in directing amyloid
fiber formation". Science 295 (5556): 851-5. PMID 11823641.
- ^ Johnson J,
Kuskowski M, Menard M, Gajewski A, Xercavins M, Garau J (2006). "Similarity
between human and chicken Escherichia coli isolates in relation to ciprofloxacin resistance status". J Infect Dis
194 (1): 71-8. PMID 16741884.
- ^ Adaptive Mutations in Bacteria: High Rate and Small Effects. Science Magazine
(10 August 2007). Retrieved on 10
September 2007.
- ^ Girard M, Steele D,
Chaignat C, Kieny M (2006). "A review of vaccine research and development: human enteric infections". Vaccine 24
(15): 2732-50. PMID 16483695.
- ^ a b Ahmed A, Li J, Shiloach Y, Robbins J, Szu
S (2006). "Safety and immunogenicity of Escherichia coli O157 O-specific polysaccharide conjugate vaccine in 2-5-year-old
children". J Infect Dis 193 (4): 515-21. PMID 16425130.
- ^ Pearson H (2007).
"The dark side of E. coli". Nature 445 (7123): 8-9. PMID 17203031.
- ^ New cattle vaccine controls E. coli infections. Canada AM (2007-01-11).
Retrieved on 2007-02-08.
- ^ Bioniche Life Sciences Inc. (2007-01-10). Canadian Research Collaboration Produces World's First Food Safety Vaccine: Against E. coli
0157:H7. Press release. Retrieved on 2007-02-08.
- ^ HPA Press
Statement: Infections caused by ESBL-producing E. coli.
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