ESCHERICHIA SPECIES




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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