Escherichia coli

3. Parathormone (PTH) :

4. General characters :
• Gram-negative rod .
• Facultative anaerobe.
• Cells are typically rod-shaped and are about 2 micrometres (μm) long
and 0.5 μm in diameter, with a cell volume of 0.6 - 0.7 μm3 .
• Named for Theodor Escherich - German physician (ca. 1885) Demonstrated
that particular strains were responsible for infant diarrhea and gastroenteritis .
• Normal flora of the mouth and intestine .
• Protects the intestinal tract from bacterial infection .
• Assists in digestion .
• Produces small amounts of vitamins B12 and K .
• Colonizes newborns GI tract within hours after birth .
• There are more than 700 different serotypes of E. coli .
• Distinguished by different surface proteins and polysaccharides .

5. • Strains that possess flagella can swim and are 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 E. coli O157:H7,
carried by a bacteriophage.

6. E. coli uses mixed-acid fermentation in anaerobic conditions,
producing lactate, succinate, ethanol, acetate and carbon
dioxide. Since many pathways in mixed-acid fermentation
produce hydrogen gas, these pathways require the levels of
hydrogen to be low, as is the case when E. coli lives together
with hydrogen-consuming organisms such as methanogens or
sulfate-reducing bacteria.

7. Many strains
• O antigen
– Somatic (on LPS)
– 171 antigens
• H antigen
– Flagella
– 56 antigens
• K antigen
– Capsule or fimbrial
antigen
– 80 antigens
O18ac:H7:K1
18th O antigen 1st K antigen
7th H antigen

8. • Healthy cattle are the major reservoir for
human infection
Deer, sheep, goats, horses, dogs, birds and flies
• Bacterial cells can survive in manure and
water troughs
• Infection is more common during the summer
in both the northern and southern
hemisphere

9. • Transmitted via food
– Ground beef
– Raw milk
– Lamb meat
– Venison jerky
– Salami and other fermented dried meat products
– Lettuce, spinach, alfalfa sprouts
– Unpasteurized apple cider
• Transmitted via water
– Drinking and swimming in unchlorinated water
• Direct person to person contact
– Diaper changing
– Improper sanitation
– Day care & chronic adult care facilities

10. Pathology

12. • Food poisoning caused by E. coli is usually caused by eating unwashed vegetables or
undercooked meat.
• 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.
• Combinations of the O & H antigens identify the serotype :

13. 1- Enteroinvasive strains:
• Biochemically, genetically, and pathogenetically closely
related to Shigella spp.
• Cause watery diarrhea
– Not bloody
• EIEC cells invade intestinal epithelial cells, lyse the
phagosomal vacuole, spread through the cytoplasm and
infect adjacent cell
– Shigella does the same thing
• Plasmid encoding a gene for a K surface antigen
– Attach and invade mucosal cells

15. 2- Enteropathogenic E coli strains:
• Attaching & effacing
• Effacement of microvilli
• Adherence between bacterium and
epithelial cells
• Unique histopathology
• Locus of enterocyte effacement

16. 16

17. 3- Enteroaggregative E. Coli:
•Adhere to HEp-2 cells.
•Human laryngeal carcinoma cells.
•Bacterial cells autoagglutinate.
•Stick to one another.
•Do not secrete enterotoxins.

19. 4- Enterhemorrhagic strain:
• Severe gastrointestinal distress
• Hemorrhagic colitis
• Crampy abdominal pain
• Watery diarrhea
• Little or no fever
• Bloody diarrhea
• New serotype O157:H7
• 1983
• Undercooked hamburgers

20. 5- Enterotoxigenic strains:
• Adhere to intestinal mucosa by fimbriae
• Produce enterotoxins
– Plasmids contain genes for enterotoxins
– Cause leakage of intestinal epithelial cells
• Loss of electrolytes & water
• Attach by fimbriae
• Cause diarrhea in children & adults
• Toxins increase intracellular levels of cAMP
• Causes cell leakage
• Traveler’s diarrhea
• Weanling diarrhea

21. E. coli is responsible for approximately 90% of urinary tract infections (UTI) seen in
individuals with ordinary anatomy. In ascending infections, fecal bacteria colonize the
urethra and spread up the urinary tract to the bladder as well as to the kidneys (causing
pyelonephritis) , or the prostate in males. Because women have a shorter urethra than men,
they are 14-times more likely to suffer from an ascending UTI.
Descending infections, though relatively rare, occur when E. coli cells enter the upper
urinary tract organs UPEC can evade the body's innate immune defenses (e.g. the
complement system) by invading superficial umbrella cells to form intracellular bacterial
communities (IBCs).They also have the ability to form K antigen, capsular polysaccharides
that contribute to biofilm formation. Biofilm-producing E. coli are recalcitrant to immune
factors and antibiotic therapy and are often responsible for chronic urinary tract infections .
K antigen-producing E. coli infections are commonly found in the upper urinary tract.
Descending infections, though relatively rare, occur when E. coli cells enter the upper
urinary tract organs (kidneys, bladder or ureters) from the blood stream.

22. It is produced by a serotype of Escherichia coli that contains a capsular
antigen called K1. The colonisation of the new born's intestines with
these stems, that are present in the mother's vagina, lead to bacteriemia,
which leads to meningitis. And because of the absence of the IgM
antibodies from the mother (these do not cross the placenta because
FcRn only mediates the transfer of IgG), plus the fact that the body
recognises as self the K1 antigen, as it resembles the cerebral
glicopeptides, this leads to a severe meningitis in the neonates.

24. In stool samples microscopy will show Gram
negative rods, with no particular cell
arrangement. Then, either MacConkey agar or
EMB agar (or both) are inoculated with the
stool.
Tests for toxin production can use mammalian
cells in tissue culture, which are rapidly killed by
shiga toxin. Although sensitive and very
specific, this method is slow and expensive .

25. E. Coli on agar media

26. EMB culture media :
Growth on Levine EMB agar produces black colonies with
greenish-black metallic sheen. This is diagnosic of E. coli.

27. MacConkey agar:
On MacConkey agar, deep red colonies are produced as the organism is lactose
positive, and fermentation of this sugar will cause the medium's pH to drop,
leading to darkening of the medium.

28. Bacterial infections are usually treated with antibiotics. However,
the antibiotic sensitivities of different strains of E. coli vary widely.
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
amoxicillin as well as other semi-synthetic penicillins , many
cephalosporins , carbapenems , aztreonam , trimethoprim-
sulfamethoxazole , ciprofloxacin, nitrofurantoin and the
aminoglycosides.