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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