E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are
harmless, this particular strain produces a powerful toxin that can cause severe illness and even death. The
combination of letters and numbers in the name of the bacterium refers to the specific markers found on its
surface and distinguishes it from other types of E. coli.
Almost everyone has some type of E. coli living in their bellies. Fortunately, most species are harmless and some
even help synthesize nutrients for us. The human bowel is usually colonized within 40 hours of birth. E. coli can
adhere to the mucus overlying the large intestine. Once established, an E. coli strain may persist for months or
Characteristics of Illness
E. coli O157 is a toxin-producing strain that can cause inflammation of the lining of the bowels and leads to the
leakage of fluid. It was not until 1935 that a strain of E. coli was shown to be the cause of an outbreak of diarrhea
E. coli 0157:H7 is the suspected cause of hemorrhagic colitus (HC) syndrome and Hemolytic Uremic Syndrome
(HUS) which is one of the most common causes of sudden, short-term kidney failure in children. HUS is the result
of a complication that can occur when the toxin produced by E. coli enters the bloodstream.
Usually presenting itself as abdominal cramps and watery diarrhea that may turn bloody. E. coli 0157 outbreaks
are believed to be passed by the fecal-oral route. It has been isolated from an increasing number of food-related
poisonings involving undercooked beef and dairy products.
E. coli O157:H7 ha been found in the intestines of healthy cattle, deer, goats, and sheep. Eating undercooked
ground beef more than any other food has caused more illnesses in the United States.
There are 5 recognized strains of E. coli that cause diarrheal disease:
enterotoxigenic E. coli (ETEC)
enteroinvasive E. coli (EIEC)
enterohemorrhagic E. coli (EHEC)
enteropathogenic E. coli (EPEC)
enteroaggregative E. coli (EAEC).
E. coli cause 90% of the urinary tract infections in anatomically-normal, unobstructed urinary tracts. The bacteria
colonize from the feces or perineal region and migrate the urinary tract to the bladder. Bladder infections are
14-times more common in females than males by virtue of the shortened urethra. The typical patient with
uncomplicated cystitis is a sexually-active female. ETEC is the most common cause of traveler's diarrhea.
0157:H7 is the most common of the enterohemorrhagic types.
About the Organism
Theodor Escherich first described E. coli in 1885, as Bacterium coli commune, which he isolated from the feces
of newborns. It was later renamed Escherichia coli, and for many years the bacterium was simply considered to
be a native organism of the large intestine.
E. coli adapts to its environment in a number of very remarkable ways considering it is a unicellular organism. For
example, it can sense the presence or absence of chemicals and gases in its environment and swim towards or
away from them. Or it can stop swimming and grow fimbriae that will specifically attach it to a cell or surface
receptor. In response to change in temperature and osmolarity, it can vary the pore diameter of its outer
membrane porins to accommodate larger molecules (nutrients) or to exclude inhibitory substances.
With its complex mechanisms for regulation of metabolism the bacterium can survey the chemical contents in its
environment in advance of synthesizing any enzymes that metabolize these compounds. It does not wastefully
produce enzymes for degradation of carbon sources unless they are available, and it does not produce enzymes
for synthesis of metabolites if they are available as nutrients in the environment.
E. coli is anaerobic when it lives intestinally and aerobic in outside environments. Wild-type E. coli has no growth
factor requirements, and metabolically it can transform glucose into all of the macromolecular components that
make up the cell. Under anaerobic conditions it will grow by means of fermentation, producing characteristic
"mixed acids and gas" as end products. However, it can also grow by means of anaerobic respiration, since it is
able to utilize NO3, NO2 .
Typical diagnosis has been done by culturing on sorbitol-MacConkey medium. However current Latex assays
and some typing antiserum have shown cross reactions with non- E. coli 0157 colonies. Furthermore, not all E.
coli strains associated with Hemolytic Uremic Syndrome (HUS) are able to ferment in sorbital.
E. coli O157 Antigen Detection ELISA Kit by IVD Research, Inc is a rapid test designed to detect a minimum
number of organisms level of 3,000 to 11,000 CFU/ml depending upon the strain of E. coli O157 present. (See
The Council of State and Territorial Epidemiologists reccomend that clinical laboratories screen at least all bloody
stools for this pathogen. The American Gastroenterological Association Foundation (AGAF) reccomended in July
1994 that all stool specimens be rountinely tested for E. coli-0157. Also, clinicians should check with their state
health department or the Centers for Disease Control and Prevention to determine which specimens should be
tested and whether the results are reportable.
Antibiotics have not proven useful in treating acute diarrheal illness. Some studies have shown that antibiotic use
may increase the chances of developing hemolytic-uremic syndrome. Treatment includes the replacement of
fluids and electrolytes to prevent dehydration, which can be especially fatal in young children. In severe cases,
acute kidney failure may require several sessions of dialysis to temporarily take over the kidneys' job of filtering
wastes from the blood. Most children recover without permanent damage to their health.
Nonprescription or prescription antidiarrheal medications usually are not recommended to treat E. coli infection.
Many antidiarrheal products slow the rate at which food and waste products move through the intestines; which
may allow more time for the body to absorb the poisons produced by the bacteria, increasing the risk of
complications such as severe blood and kidney problems. A health professional may prescribe one of these
medications if he or she does not know E. coli caused the diarrhea.
Prevention is the Best Cure
Scrubbing or rinsing your vegetables is important since E. coli is found in many animals including sheep, goats
and cattle whose manure is often used in the fertilization process.
The virus infects people through eating undercooked meat, so even if you like your meat bloody, it is wise to
order your meal cooked thoroughly. The meat must reach 160 degrees to be considered fully cooked. Cross
contamination can spread the bacteria in your kitchen, so it is always important to use two different knifes for
meat and vegetable preparation.
Another method of prevention is to teach children how important their personal hygiene is. Children can spread
viruses and bacteria between themselves at school and daycare centers extremely easily. Make sure they know
to wash their hands thoroughly after using the bathroom, or having been in the playground and why it is
important to do so.