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Pathogenic Escherichia coli
Escherichia coli commonly is a Gram-negative, rod-shaped bacterium that is commonly found in
the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless,
but some serotypes are pathogenic can cause serious food poisoning in humans, and are
occasionally responsible for product recalls.[1][2] The harmless strains are part of the normal flora
of the gut, and can benefit their hosts by producing vitamin K2,[3] and by preventing the
establishment of pathogenic bacteria within the intestine.[4][5]
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Introduction
E. coli and related bacteria constitute about 0.1% of gut flora,[6] and fecal-oral transmission is the
major route through which pathogenic strains of the bacterium cause disease. Cells are able to
survive outside the body for a limited amount of time, which makes them ideal indicator
organisms to test environmental samples for fecal contamination.[7][8] The bacterium can also be
grown easily and inexpensively in a laboratory setting, and has been intensively investigated for
over 60 years. E. coli is the most widely studied prokaryotic model organism, and an important
species in the fields of biotechnology and microbiology, where it has served as the host organism
for the majority of work with recombinant DNA.
German paediatrician and bacteriologist Theodor Escherich discovered E. coli in 1885,[7] and it is
now classified as part of the Enterobacteriaceae family of gamma-proteobacteria.[9]
Serotype
Pathogenic E.coli strains can be categorised based on elements that can elicit an immune response
in animals, namely:
1. O antigen: part of lipopolysaccharide layer
2. K antigen: capsule
3. H antigen: flagellin
4. F antigen: MR fimbriae (rare)
For example E.coli strain EDL933 is of the O157:H7 group.
O antigen
The outer membrane of an E. coli cell contains millions of lipopolysaccharide (LPS) molecules,
which consists of:
1. O antigen, a polymer of immunogenic repeating oligosaccharides (1–40 units)
2. Core region of phosphorylated nonrepeating oligosaccharides
3. Lipid A (endotoxin)
The O antigen is used for serotyping E.coli and these O group designations go from O1 to O181,
with the exception of some groups which have been historically removed, namely O31, O47,
O67, O72, O93 (now K84), O94, and O122; groups . The O antigen is encoded by the rfb gene
cluster. rol (cld) gene encodes the regulator of lipopolysaccharide O-chain length.
K antigen
The acidic capsular polysaccharide (CPS) is a thick, mucous-like, layer of polysaccharide that
surrounds some pathogen E. coli...
There are two separate groups of K-antigen groups, named group I and group II
Group I K antigens are only found with certain O-antigens (O8, O9, O20, and O101 groups),
Group II K antigens closely resemble those in Gram positive bacteria and greatly differ in
composition . In total there are 60 different K antigens
H antigen
The flagella allows E. coli to move. H antigens groups go from H1 to H56 with some exceptions
(H13 and H22 were not E. coli antigens but from Citrobacter freundii, also a coliform, and H50
being the same as H10). These are encoded by the fliC gene.
Role in disease
In humans and in domestic animals, virulent strains of E. coli can cause various diseases.
In humans : gastroenteritis, urinary tract infections, and neonatal meningitis. In rarer cases,
virulent strains are also responsible for haemolytic-uremic syndrome, peritonitis, mastitis,
septicaemia and Gram-negative pneumonia.[11]
Gastrointestinal infection
Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times.
Each individual bacterium is a rounded cylinder.
Certain strains of E. coli, such as O157:H7, O104:H4, O121, O26, O103, O111, O145, and
O104:H21, produce potentially lethal toxins. Food poisoning caused by E. coli can result from
eating unwashed vegetables or undercooked meat. O157:H7 is also notorious for causing serious
and even life-threatening complications such as hemolytic-uremic syndrome. This particular
strain is linked to the 2006 United States E. coli outbreak due to fresh spinach. The O104:H4
strain is equally virulent. Antibiotic and supportive treatment protocols for it are not as welldeveloped (it has the ability to be very enterohemorrhagic like O157:H7, causing bloody diarrhea,
but also is more enteroaggregative, meaning it adheres well and clumps to intestinal membranes).
It is the strain behind the deadly June 2011 E. coli outbreak in Europe. Severity of the illness
varies considerably; it can be fatal, particularly to young children, the elderly or the
immunocompromised, but is more often mild. Earlier, poor hygienic methods of preparing meat
in Scotland killed seven people in 1996 due to E. coli poisoning, and left hundreds more infected.
E. coli can harbour both heat-stable and heat-labile enterotoxins.
If E. coli bacteria escape the intestinal tract through a perforation (for example from an ulcer, a
ruptured appendix, or due to 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 gentamicin. Recent research suggests treatment of
enteropathogenic E. coli with antibiotics may not improve the outcome of the disease[citation needed],
as it may significantly increase the chance of developing haemolytic-uremic syndrome.[13]
Intestinal mucosa-associated E. coli are observed in increased numbers in the inflammatory
bowel diseases, Crohn's disease and ulcerative colitis.[14] Invasive strains of E. coli exist in high
numbers in the inflamed tissue, and the number of bacteria in the inflamed regions correlates to
the severity of the bowel inflammation.[15]
Epidemiology of gastrointestinal infection
Transmission of pathogenic E. coli often occurs via faecal-oral transmission.[18][19][20] Common
routes of transmission include: unhygienic food preparation,[19] farm contamination due to manure
fertilization,[21] irrigation of crops with contaminated greywater or raw sewage,[22] feral pigs on
cropland,[23] or direct consumption of sewage-contaminated water.[24] Dairy and beef cattle are
primary reservoirs of E. coli O157:H7,[25] and they can carry it asymptomatically and shed it in
their faeces.[25] Food products associated with E. coli outbreaks include cucumber,[26] raw ground
beef,[27] raw seed sprouts or spinach,[21] raw milk, unpasteurized juice, unpasteurized cheese and
foods contaminated by infected food workers via faecal-oral route.[19]
According to the U.S. Food and Drug Administration, the faecal-oral cycle of transmission can be
disrupted by cooking food properly, preventing cross-contamination, instituting barriers such as
gloves for food workers, instituting health care policies so food industry employees seek
treatment when they are ill, pasteurization of juice or dairy products and proper hand washing
requirements.[19]
Shiga toxin-producing E. coli (STEC), specifically serotype O157:H7, have also been transmitted
by flies,[28][29][30] as well as direct contact with farm animals,[31][32] petting zoo animals,[33] and
airborne particles found in animal-rearing environments.[34]
Name:_______________________________________________________
E.coli Questions from Powerpoint and reading
1. Where does nonpathogenic E.coli normally reside?
2.
What is a benefit of having E.coli as normal microbial flora?
3. Explain the term “model organism”.
4. Describe how E.coli is used to produce a protein such as insulin.
5. Describe the 2 factors that can make E.coli a virulent organism.
6.
What are the 3 antigens used to type E.coli and where are these antigens located on the
organism?
7. What types of diseases can be caused by E.coli?
8.
What is the mode of transmission for gastrointestinal diseases?
9.
How do enterotoxins work?