enterobacteriaceae ii - microscopic appearance - cultural characteristics - biochemical tests of...
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Enterobacteriaceae II
- Microscopic appearance
- Cultural characteristics
- Biochemical Tests of Enterobacteriaceae (Non-
Lactose fermenters).
- Identification of Enterobacteriaceae using API 20E
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Enterobacteriaceae
- Gram negative rods
- Aerobes and facultative anaerobes
- Motile and non-motile
- Oxidase negative
- Reduce nitrate to nitrite
- Ferment glucose with acid production
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Enterobacteriaceae
Lactose fermenting Non-Lactose fermenting
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Non-Lactose fermenting
Salmonella
Shigella
Proteus
Morganella
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Shigella
-Shigellae infect only humans causing
bacillary
dysentery [ Shigellosis ].
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poor sanitation
unhygienic conditions
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Contaminated food & drink
overcrowding
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-A fresh faecal specimen is required to isolate Shigella
species.
-When there is likely to be a delay in the specimen reaching the
laboratory a suitable transport medium must be used to
ensure
viability of the organisms.Carry Blair Transport Medium
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- Specimens have an alkaline pH unlike those from patients
with
amoebic dysentery which have an acidic pH.
- faecal specimens may be watery and contain little blood,
mucus,
and pus cells. In the later stages, the specimen may consist
entirely of pus and blood mixed with mucus.
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Shigellae are Gram negative rod.
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Shigellae are non-motile organisms
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On MacConkey agar Shigella species producing pale non-
lactose fermenting colonies.
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On KIA (Kligler iron agar) Most strains of Shigellae produce red
slope and yellow butt. [tube No. 2]
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- Enteric fever [ Typhoid & Paratyphoid].
- Diarrhoeal disease [enterocolitis].
- Bacteraemia.
Salmonellae
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• specimens include blood, faeces, and urine for
culture as follow :-
1- Blood: Organisms can usually be detected during the
first ten days of infection.
*** S. Typhi can be more rapidly and successfully isolated
from
bone marrow than from blood, especially if the patient has
been treated with antibiotics.
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2- Faeces: Organisms can usually be isolated from 40–50% of
patients during the second week of infection and from about
80% of patients during the third week. Faecal culture is
useful
for detecting S. Typhi carriers.
3- Urine: Organisms can usually be isolated from about 25% of
patients after the second week of infection.
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Salmonellae are Gram negative rods, non-motile.
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On Blood agar Salmonellae produce grey-white 2-3 mm in
diameter, non-haemolytic, some strains appear mucoid.
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On MacConkey agar Salmonellae produce pale non-lactose
fermenting colonies.
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On Deoxycholate Citrate agar (DCA) Salmonellae produce pale colonies have black centres (H2S-producing Salmonellae).
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1- S.Typhi produce red slope yellow butt with few amount of H2S2- S.Paratyphi A produce red slope yellow butt without H2S production3- S.Paratyphi B produce red slope yellow butt with high amount of H2S
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Proteus
- Urinary Tract Infection. ( urine )*
- Septicaemia. ( blood )*
- Abdominal & wound Infections. ( Pus )*
- Chest infection. ( sputum )*
* Specimens depending on site of infection.
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- Proteus is Gram negative rod
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Proteus are actively motile
organisms ( swarming
phenomenon)
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Proteus are actively motile organisms
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On MacConkey agar Proteus are non-lactose fermenting,
producing pale colonies.
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Vogues Proskauer Test
- used to detect acetoin in a bacterial broth culture
- The test is performed by adding alpha-naphthol
and potassium hydroxide to the Voges-Proskauer
broth which has been inoculated with bacteria. A
cherry red color indicates a positive result, while a
yellow-brown color indicates a negative result
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- digestion of glucose to acetylmethylcarbinol. If glucose is
being broken down, it will react with alpha-naphthol (VP
reagent 1) and potassium hydroxide (VP reagent 2) to form a
red color. Alpha-naphthol and potassium hydroxide are
chemicals that detect acetoin.
Vogues Proskauer Test
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- The test is based on the ability of an organism to use citrate
as its only source of carbon.
CitrateUtilization Test
-Bacteria that can grow on this medium turn the
Bromothymol
blue indicator from green to blue.
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When bacteria cultured in a medium which contains tryptophan.
Indole production is detected by Kovac’s reagent which contains 4
(p)-dimethylaminobenzaldehyde which reacts with the indole to
produce a red coloured compound.
Indole Production
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When the strain is urease producing, the enzyme will break down
the urea (by hydrolysis) to give ammonia and carbon dioxide.
With the release of ammonia, the medium becomes alkaline as
shown by a change
in colour of the indicator to pink-red.
Urease Test
The test organism is
cultured in a medium which
contains urea and the
indicator phenol red.
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Biochemical tests of Enterobacteriaceae