Escherichia coli is a Gram negative bacteria, rod shaped bacterium that is commonly found in the lower intestine warm blooded organisms (endogens). Most Escherichia coli strains are harmless, but some serotypes can cause food poisoning in humans, and are occasionally responsible for product recalls. The harmless strains are part from the normal flora of the gut. They can benefit their hosts by producing vitamin K2 and by preventing the establishment of pathogenic bacteria within the intestine.
Escherichia coli and related bacteria constitute about 0,1% of gut flora, and fecal oral transmission is the major rout trough 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. There is, however, a growing body of research that has examined environmentally persistent E. coli which can survive for extended periods of time outside the host. The bacterium can also be grown easily and expensively 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 recombination of DNA.
As we said Escherichia Coli is a gram negative bacteria, facultative anaerobic and non-sporulating.Cells are typically rod-shaped, and are about 2,0 microns long and 0,5 microns in diameter , with a cell volume of o,6 – o,7 (um)3. It can survive a wide variety of substrates. E. Coli uses mixed – acid fermentation in anaerobic condition, producing lactate, succinate, ethanol, acetate and carbon dioxide. Since many pathways in mixed – acid fermentation produce hydrogen gas these pathways require the level of hydrogen to be low, as is the case when E. Coli lives together with hydrogen consuming organisms, such as methanogens or sulphate – reducing bacteria.
Optimal growth of E. Coli occurs at 37 C but some laboratory strains can multiply at temperatures up to 49 C. Growth can be driven by aerobic or anaerobic respiration , using a large variety of redox pairs , including the oxidation of pyruvic acid , formic acids, and the reduction of substrates such as oxygen, nitrate, dimethyl sulfoxide and trimethylamine N –oxide. Starins that possess flagella and motile. The flagella have a peritrichous arrangement. E. Coli and related bacteria possess the ability to transfer DNA via bacterial conjugation, transduction or transformation, which allows genetic material to spread horizontally through an existing population. This process led to the spread of the gene encoding shiga toxin from Shigella to
Escherichia coli carried by a bacteriophage.
More than 700 serotypes of E.Coli have been identified. The “O” and the “H “antigens of their bodies and flagella distinguish the different E. Coli serotypes, respectively. The E. Coli serotypes, that are responsible for the numerous reports of outbreaks traced to the consumption of contaminated foods and beverages are those that produce Shina toxin (Stx), so called because the toxin is virtually identical to that produced by another bacteria known as Shigella dysenteria type 1 (that also causes body diarrhea and hemolytic uremic syndrome (HUS) in emerging countries like Bangladesh). It is important to remember that most kinds of E. Coli do not cause disease in humans, indeed, some are beneficial, and some cause infections, such as urinary tract infections. This section deals specifically with Stx – producing E. coli including specifically E. coli O157: H7.
Shiga toxin is one of the most potent toxins known to man. This toxin is so potent that the Center of Disease Control and Prevention considers it as a potential bioterrorist agent. It seems likely that DNA from Shiga toxin producing Shigella bacteria can be transferred by a bacteriophage (a virus that infects bacteria) to otherwise harmless E. Coli bacteria providing them with the genetic material to produce Shiga toxin.
Although E. Coli O157 : H7 is responsible for the majority of human illnesses attributed to E. coli there are additional STX- producing E. coli (e.g , E. coli O121 : H 19 ) that can also cause hemorrhagic colitis and post- diarrheal hemolytic uremic syndrome (D+ HUS). HUS is a syndrome that is defined by the trilogy of hemolytic anemia ( destruction of the red blood cells ), thrombocytopenia (low platelet count ) and acute kidney failure.
Stx producing E. coli organisms have several characteristics that make them so dangerous. They are
hardly organisms that can survive several weeks on suffices such as counter tops , and up to a year
in some materials like compost. They have a very low infectious dose meaning that only a relatively
small number of bacteria ( fewer than 50 ) are needed to set up housekeeping in a victim’s intestinal
tract and cause infection .
In most infected individuals, the symptoms of E. coli infection last about a week and resolve without
any long – term problems. Antibiotics do not improve the illness, and some medical researchers
believe that these medications can increase the risk of developing post- diarrheal hemolytic uremic
syndrome (D+ HUS).
Therefore, apart from good supportive care, such as close attention to hydration and nutrition ,
there is no specific therapy to halt E. coli symptoms . The recent finding that E. coli O157 H :7 initially
speeds up blood coagulation may lead to future medical therapies that could forestall the most
serious consequences . Most individuals who do not develop D+HUS recover within two weeks.
E. coli O157 : H7 was first recognized as a forborne pathogen in 1982 during an investigation into an
outbreak of hemolytic colitis (bloody diarrhea) associated with the consumption of contaminated
hamburgers. The following year, Shiga toxin produced by the small tenths, known as E. coli O157
H:7, was identified as the real culprit .
Since there is no safe food safety program, consumers need to “drive defensively” as they navigate
from the market to the table. It is no longer sufficient to take precautions only with ground beef and
hamburgers, anything ingested by family members can be a vehicle for infection.
Shiga toxin producing E. coli are now so widely disseminated that a wide variety of foods can be
contaminated. Direct animal –to- person and person -to – animal transmission is not uncommon.
Following are steps you can take to protect your family.
Irradiation offers the most practical and effective way of sterling foods and protecting the
consumer. It is already being used for poultry, and is approved for all other food. Even though
the word “irradiation“conjures up fears of radiation exposure, irradiation food does not
become “radioactive”, it is safe and does not change the taste or texture of the food. To insure
safety, the public needs to be educated and the food industry should be convinced that this will
not only protect the consumer, but will also favorably affect the bottom line. This should be a “no
brainer” given the fact that contaminated foods are costing the food industry hundreds of millions of
dollars a year.