Enterobacteria are Gram-negative bacteria in the family Enterobacteriaceae, including pathogenic E. coli. E. coli can cause urinary tract infections, neonatal meningitis, and intestinal diseases. There are five classes of pathogenic E. coli that cause diarrhea - enterotoxigenic E. coli, enteroinvasive E. coli, enterohemorrhagic E. coli, enteropathogenic E. coli, and enteroaggregative E. coli - each with distinct pathogenic mechanisms. E. coli is diagnosed through culture, biochemical tests, and examining reactions on media like MacConkey agar and triple sugar iron agar. Treatment depends on the site and strain of infection.

1. ENTEROBACTERIA &
Pathogenic E. coli
Prof. Abbas Hayat
Gram negative bacteria which belong
to the family Enterbacteriaceae.
Also called coli forms.

5. MacConkey Medium :

6. Rapid presumptive identification of Gram
negative bacteria.
Lactose fermenters
Pink colonies on Mac Conkeys media
1. Escherichia coli Metallic sheen on EMB,
Motile No viscous colonies
2. Enterobacter species Raised colonies .Non
viscous colonies
3. Klebseilla species Very viscous mucoid Non
motile

7. Slow lactose fermenters on Mac Conkeys
media 48 hours .
•Citrobacter
•Serratia
•Providencia
• Arizona. etc.
``opportunist pathogens``

9. Non Lactose fermenters
Colorless colonies on Mac Conkeys
• Shigella species: Non motile
• Salmonella species: Motile
• Proteus species: Swarming, urea hydrolyzed.
• Pseudomonas species: Green pigment sweetish
smell.

10. 1. Morphology and staining
Gram negative rods , motile or non motile,
peritrichous flagella, non sporing.
2. Culture:
a. Mac Conkeys medium
b. EMB (Eosin Methylene Blue agar)
c. Blood agar
d. CLED (Cystien Lactose Electrolyte Deficient
Medium)

11. 3. Biochemical characteristics:
• a. Lactose fermentation
• b. Reduce nitrates to nitrites
• c. Ferment glucose
• d. Oxidase negative

12. • 1. Indole test: E. coli produces indole
• 2. Methyl red: indicates pH of culture if
below 4.5 positive.
• 3. Voges –Proskere reaction:
Depends on production of
acetylmethylcarbinol from dextrose gives
pink color positive in Enterobacter.
• 4. Citrate test: Utilization of sodium citrate
as sole source of carbon Klebseilla positive.

13. MNEMONIC FORMULA:
• IMViC for E. coli is ++--,
• Enterobacter is --++.
Other tests:
1. Triple Sugar Iron or TSI medium
2. Urease production

14. • TRIPLE SUGAR IRON (TSI ) AGAR REACTION
One such medium is TSI.
• Medium contains 0.1 % glucose 1 % sucrose 1 %
lactose ,Ferrous sulphate ( for detection of H2S,
production ) and a pH indicator ( phenol red ).
• Pored into test tube to produce a slant and a deep
butt If only glucose is fermented , the slant and butt
initially turn yellow from the small amount of acid
produced ;
as the fermented products are subsequently oxidized
the slant turns Alkaline ( RED).
• If lactose or sucrose is fermented so much acid is
produced that slant and butt remain Acid
(YELLOW).

16. TSI(Medium reactions) Escherichia coli - a facultative
anaerobe, ferments both glucose and lactose as a carbon
source, produce gas, but does not produce hydrogen
sulfide

17. Salmonella enteritidis (serotype typhimurium) can
ferment glucose but not lactose as carbon source
and produces both hydrogen sulfide and gas.

18. Coliforms and Public Health:
• Contamination of Public water by
sewerage is detected by presence of
E. coli Klebsiella and Enterobacter
• Mainly E. coli is used as an indicator
of unaccepted faecal contamination.
Colony count > 4 dL.

22. Washing hands with sewerage water

35. End of Introduction to
Enterobacteracaie.
SMS sent by someone
`` A perfect lecture should be like a
girls skirt. Which iz long enough to
cover the subject and short enough
2 create interest``

36. Should we continue
with E. coli ?

37. Diseases Caused
by
E. COLI

38. • Habitat: E. coli is the head of the
large bacterial family the
Enterbacteriacae.
Which consists of enteric bacteria,
which are facultative anaerobic
Gram-negative rods that live in the
intestinal tracts of animals in health
and disease.

39. Pathogenesis of E. coli
Over 700 antigenic types or serotypes of E. coli have
been recognized based on O, H, and K antigens.
E. coli is responsible for three types of infections in
humans:
• 1. Urinary tract infections (UTI).
• 2. Neonatal meningitis.
• 3. Intestinal diseases (gastroenteritis) and Sepsis.
These diseases depend on a specific array of
pathogenic (virulence) determinants

40. Urinary tract infections
• Uropathogenic E. coli causes 90% of the
urinary tract infections (UTI) in
anatomically-normal, unobstructed urinary
tracts.
• Bladder infections are 30-times more
common in females of child bearing age
than males by virtue of the shortened
urethra.

42. • The typical patient with uncomplicated
cystitis is a sexually-active first colonized in
the intestine with an
Uropathogenic E.
coli strain.
• Organisms propelled into the bladder from
the peri urethral region during sexual
intercourse. With the aid
of specific adhesins they are able
to colonize the bladder.

43. • Neonatal meningitis affects1/2,000-4,000
infants. Eighty percent of E. coli strains
involved synthesize K-1 capsular antigens
(K-1 is only present 20-40% of the time in
intestinal isolates).
• E. coli strains invade the blood stream of
infants from the nasopharynx or GI tract
and are carried to the meninges.

44. E. coli strains invade the blood stream of
infants from the nasopharynx or GI tract
and are carried to the meninges.

45. • E. coli strains invade blood stream of infants from
the nasopharynx or GI tract and carried to the
meningitis.
• Epidemiologic studies show that pregnancy
associated with increased rates of colonization by
K-1 strains involved in the subsequent cases of
meningitis in the newborn. GI tract is the portal
of entry into the bloodstream.
• Colonization is fairly common, invasion and the
catastrophic sequelae are rare.
• Neonatal meningitis requires antibiotic therapy
that usually includes ampicillin and a third-
generation cephalosporin

46. Gastrointestinal
Disease

47. Intestinal diseases caused by E. coli
As a pathogen, E. coli, of course, is best known for its
ability to cause intestinal diseases.
Five classes of E. coli that cause diarrhea are now
recognized:
• Enterotoxigenic E. coli (ETEC),
• Enteroinvasive E. coli (EIEC),
• Enterohemorrhagic E. coli (EHEC),
• Enteropathogenic E. coli (EPEC), and
• (EAggEC).
Each class falls within a serological subgroup
and manifests distinct features in
pathogenesis.

48. • ETEC an imp. cause of diarrhea in infants and travelers in
underdeveloped countries.
• EIEC resemble Shigella in their pathogenic mechanisms and
illness they produce.
• EPEC induce watery diarrhea similar to ETEC.
• The distinguishing feature of EAggEC strains is their ability
to attach to tissue culture cells in an aggregative manner.
These strains are associated with persistent diarrhea in
young children.
• EHEC causes a diarrheal syndrome, there is copious
bloody discharge and no fever. Frequent life-threatening
situation is its toxic effects on the kidneys (hemolytic
uremia).
EHEC has recently been recognized as a cause of serious
disease (e.g. the Jack-in-the-Box outbreak in the
Northwest).Pediatric diarrhea caused by this strain can be
fatal due to acute kidney failure
(hemolytic uremic syndrome [HUS]).

50. Treatment:
• Depends on site of disease and resistance pattern.
• Uncomplicated UTI 1-3 days with oral Trimethoprim-
Sulfamethaxazole or an oral Penicillin, Amoxil /Ampicillin.
• E. coli sepsis: Parental antibiotics e.g. Amino glycoside
gentamicin or a cephalosporin.
• Neonatal meningitis: Combination of ampicillin and
gentamicin or a third or fourth generation cephalosporin.
• E. coli diarrheal disease: Antibiotics usually not indicated.
Timethoprim – Sulfamethaxazole may shorten duration.
• Rehaydration more imp. Self limiting.

51. Lab Diagnosis:
• Specimens: Stool, Urine, Blood, Pus, C.S.F.
Food, and Water.
• Culture: Blood agar and a differential
medium like Mac Conkeys medium
• Biochemical Tests; IMViC,. T.S.I reactions
Citrate utilization, Sugar fermentations etc.

52. Prevention and Control.
1. No specific prevention No
active or Passive Vaccination.
2. General measures:
Removal of catheters, Prophylaxis with urinary
antiseptics like Nitrofurantoin.
3. Caution regarding food and water.