ESCHERICHIA SPECIES

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ESCHERICHIA





Define Escherichia 
A Gram negative rod .
 List the species of Escherichia
  • Esherichia  coli
  • Escherichia  blattee
  • Escherichia  fergusonii
  • Escherichia  vulneris
  • Escherichia  hermanii

 Mention the species of medical importance
  • Esherichia  coli
  
  • Describe the normal habitat Esherichia  coli

—  It forms the normal flora of the intestinal tract of humans and animals.
—  They are also found in water,soil and vegetation
 Describe the morphology Esherichia  coli 
  • Gram –ve rods.
  • Motile with peritrichous flagella
  • Non- sporing
  • Some strains are capsulated
  • Measures about 2-3um in length and 0.3um in width
               


 Describe the mode of transmission and pathogenicity of Esherichia  coli

Esherichia  coli is transmitted :-
  • By ingestion of contaminated food or water.
PATHOGENICITY-
Esherichia  coli causes:-

•      Causes infections in human and animals.
•      The infections are:-
–     Gastroenteritis
–     Urinary tract infections(Cystitis,pyelonephritis)
–     Appedicitis
–     Gall bladder infection
–     Bcteraemia
–     Menigitis of the new born.
–     Pyogenic infections(wound infections)
–     Septicaemia
–     Diarrhoae in infant and adult(ETEC)

 Explain the strains of Esherichia  coli 
There are 5 strains(groups) of E.coli that causes diarrheal diseases:-
·         Entero toxigenic E.coli(ETEC)
Ø  Causes watery diarrhea in infants and young children. They cause travelers diarrhea.
Ø  They produce Enterotoxins of two types i.e -Heat stable toxins(non antigenic
-Heat labile toxin(antigenic)
Ø  Both toxins inhibit active intestinal absorption and stimulate secretion of water and electrolyte in to the lumen. This is enhanced by Adenyl Cylase enzyme known as CAMP.



·         Enteropathogenic E.coli(EPEC)
Ø  It causes out break of infantile diarrhea(infant).
Ø  They can cause severe Diarrhoea in adult
·         Entero invasive E.coli(EIEC)
Ø  This strain resemble Shigella in their biochemical reactions.
Ø  It invades the mucosal of small intestines(ileum) and colon and cause dysentery.
Ø  Specimen contains blood,pus and mucus
OTHERS
·         Enterohaemorrhagic E.coli(EHEC)

·         Verocytogenic E.coli(VCEC)

Describe the laboratory diagnosis Esherichia  coli 
1.SPECIMENS
  • Stool
  • urine
  • pus
URINE
  • Inoculate in CLED media.
  • Incubate for 18-24 hrs  AT 370C.
  • Check for yellow shiny colonies(LF)
PUS
  • Inoculate on BA and MACC.
  • Incubate for 18-24 hrs  AT 370C.
  • Check for B-hemolytic colonies that are 1-2mm in diameter and are also shiny and cream
MACCONKEY AGAR
  • Incubate 18- 24 hrs  at 370c.
  • Check for pink colonies ,2-3 mm in diameter.(LF)
2.CULTURE CHARACTERISTICS



i)MACCONKEY AGAR
  • Pink/rossy pink colconies are seen.
  • The colonies are large 2-3mm in diameter.
  • The colonies are translucent.
ii)CLED
  • Large yellow colonies are produced(LF)
  • They measure 2-3mm in diameter.
iii)BLOOD AGAR
  • Pale yellow beta haemolytic colonies are produced.
iv)NUTRIENT AGAR
  • Smooth,colourless colonies which are easly emulsified are seen.
    • .
3.BIOCHEMICAL TESTS
FOR  Esherichia  coli:-Perform Biochemical tests to identify the organisms
Perform the following tests for E.coli:-
  • Indole +ve                                          
  • MR +ve                                               
  • Motility  +ve                                       
  • Citrate  -ve                                         
  • Ferments-glucose,lactose,fructose,mannitol,
  • Maltose and inositol is not fermented
  • ONPG     +ve
  • TSI-  A/A+ gas no H2s
  • urease –ve
  • VP -Ve
SUMMARY OF BIOCHEMICAL TESTS REACTION
  • I-indole=  +VE
  • M-methyred= +VE
  • V-voges prousker= -VE
  • C-Citrate= -VE
  • O-ONPG= +VE
4.PREVENTION

  • Seek medical treatment
  • Hygiene
  • Breastfeeding infants instead of using bottles
  • Isolation of the infected
  • Screening before admission
  • Proper cooking and storage of food 

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