Monday, December 10, 2007

Biochemical tests for bacteria indentification-Group post 2

Biochemical tests for gram negative bacteria identification


-measure the ability to hydrolyse and deaminate tryptophan

-Klesiella-enterobacter-salmonella-serratia are mostly negative

-positive-red colour

2)Methyl red

-methyl red, a pH indicator with a range between 4.4(red) and 6.0(yellow)

-only species that produce suffiicient acids can maintian the pH at below4.4 against the buffer system of the test medium

-most species of Enterobacteriaceae produce strong acids. Enterobacter-serratia do not produce enough acids

-positive-stable red colour in the surface layer of the medium

3)Voges-proskauer reaction test

-this test is based on the conversion of acetoin to a red coloured complex through the action of KOH, atmospheric 02 and alpha napthol

-Klesiella-enterobacter-serratia is able to perform this pathway

-red colour at the surface of the medium after 15 mins following the addition of reagents

4)Citrate utilisation test

-some bacteria have the ability to utilize citrate as the sole carbon sourc and turn the medium allkaline due to production of ammonia

-Escherichia-Edwardisella-shigella-salmonella cannot utilise citrate as the sole source of carbon

-positive-from colour green to blue

5)Urease test

-some species posses the enzyme urease and able to hydrolyze urea with the release of ammonia and carbon dioxide

-this is used mainly to differentiate urease positive Proteus species from other member of Enterobacteriaceae

-positive-yellowish orange to pink

Biochemical tests for gram positive bacteria

1)Oxidase test

-this is to differentiate those that possess the enzyme cytochrome oxidase c from those that lack of the enzyme

-useful in screening for bacteria species which belong to the Enterobacteriaceae or the Pseudomonas genus

-positive-development of purple colour

2)Coagulase test

-the coagulase test is used to differentiate staphylcoccus aures from other staphylcoccus species

-positive-clot forms

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