| Decarboxylation Tests |
DESCRIPTION
Decarboxylation test is used to determine bacteria's ability to decarboxylate amino acids. Most used amino acids
are arginine, lysine and ornithine. To induce the decarboxylase enzymes both the substrate (amino acids) and
acidic conditions are required.
Decarboxylation test is used to determine bacteria's ability to decarboxylate amino acids. Most used amino acids
are arginine, lysine and ornithine. To induce the decarboxylase enzymes both the substrate (amino acids) and
acidic conditions are required.
MEDIUM PREPARATION
Composition: peptone 5 g, meat extract 5 g, bromcresol purple 1.6%
(0.625 ml); cresol red 0.2% (2.5 ml), glucose 0.5g, pyridoxal phosphate 5
mg, distilled water 1000 ml. Add 1% L-lysine or 1% L-arginine or 1%
L-ornithine.
Adjust pH to 6-6.5.
PROCEDURE
Inoculate germs from a young culture, add mineral oil and incubate at 37
°C. Read results after 24 hours; purple medium for positive and yellow for
negative.
EXPLANATION
First the glucose is fermented with acid production, turning the medium
yellow. Then the decarboxylase enzyme hydrolyses the amino acids
increasing the pH. The high pH level turns the medium purple.
Composition: peptone 5 g, meat extract 5 g, bromcresol purple 1.6%
(0.625 ml); cresol red 0.2% (2.5 ml), glucose 0.5g, pyridoxal phosphate 5
mg, distilled water 1000 ml. Add 1% L-lysine or 1% L-arginine or 1%
L-ornithine.
Adjust pH to 6-6.5.
PROCEDURE
Inoculate germs from a young culture, add mineral oil and incubate at 37
°C. Read results after 24 hours; purple medium for positive and yellow for
negative.
EXPLANATION
First the glucose is fermented with acid production, turning the medium
yellow. Then the decarboxylase enzyme hydrolyses the amino acids
increasing the pH. The high pH level turns the medium purple.
NOTES:
If the test is incubated more than 24 hours then organisms start using the peptone, the resulted products increase
the pH and false positive results may be obtained.
If the test is incubated more than 24 hours then organisms start using the peptone, the resulted products increase
the pH and false positive results may be obtained.
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