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Biochemical Test

Agar Plates

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Biochemical Test
Agar Plates
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Urease test
References

MacConkey Agar

 

    MacConkey agar is widely used to examine stools specimens. To shut out the proliferation of gram-positive bacteria, 1 mg per liter of crystal violet is included in the composition. Similarly, 30 mg per liter of neutral red is used to act as pH indicator. In the fermentation of lactose by gram-negative bacteria, an acid is produced, in this case, giving their colonies a red colouration; a colourless colony indicates that the bacteria there do not ferment lactose.

 

Hektoen-enteric Agar

 

    Hektoen Enteric (HE) agar is recognised for a much improvised bacterial colonial differentiation due to its effectiveness in exposing high-speed lactose-fermenting organism in fecal specimens. Additional capabilities include the detection of hydrogen sulphide producers. HE agar encompasses 3 carbohydrates – lactose, salicin, and sucrose and in addition, indicator dyes including Bromthymol blue (65 mg per liter) and acid fuchsin (100 mg per liter). Against the faint pink to red background of the medium, high-speed lactose-fermenting bacteria shows up as bright yellow to salmon-pink glistening drops. Nonlactose fermenters are normally blue-green to green in colour, Sodium thiosulfate and ferric ammonium citrate are employed in the medium to reveal the presence of H2S emitters, which will have black centers in their colonies. It is crucial to ensure that the HE agar is transparent and green in colour before use.

 

Mannitol-salt Agar

 

Based on the purpose of isolating and differentiating of pathogenic Staphylococcus aureus, Mannitol-salt agar was customized by concocting a solution of 7.5% Sodium Chloride. The very basis of its function: it inhibits the proliferation of most bacteria. The medium also include 10g of mannitol per liter for the identification of mannitol fementation. Phenol is added into the medium in the concentration of 25mg per liter.

 

Blood Agar

 

A blood agar plate can be made from any animal blood. However results may alter depending on the different animal blood agars used. Thus, clinical results use 5-10% sheep blood agar plates as the standard for defining hemolytic reaction of bacteria.

 

Blood Agar
bloodagar.jpg
http://www.madsci.org/~lynn/micro/media

Mac-Conkey
macconkey.jpg
http://www.madsci.org/~lynn/micro/media

Hektoen-Enteric Agar
hektoenentericagar.jpg
http://www.madsci.org/~lynn/micro/media

Mannitol-Salt Agar
mannitolsaltagar.jpg
http://faculty.ivytech.edu/~bsipe/UNKN/230_files/image004.jpg