Amino acid and protein metabolism

1.
Indigo substrate test Some bacteria can decompose tryptophan in peptone to produce indole
.
The presence of indole can be demonstrated by a color reaction

Test method: Inoculate a small amount of the pure culture to be tested in tryptophan broth medium.
After incubating at (36±1)°C for 24 hours, take about 2 mL of the culture solution and add 2 to 3 drops of Kovacs' reagent.
Shake the test tube until it is red, or add a small amount of ether or xylene .
Shake the test tube to extract and concentrate the spin matrix.
After it floats on the surface of the culture medium, slowly add a few drops of Kovacs' reagent along the wall of the test tube.
If the face is red, it is positive
.

2.
Amino acid decarboxylase test Bacteria with amino acid decarboxylase can make amino acids produce amines, increase the pH of the medium, and make the medium indicator color
.
If the culture medium turns purple, it is a positive reaction, while the culture medium does not change color and it is a negative reaction.

3.
Hydrogen sulfide test Some bacteria can decompose sulfur-containing amino acids to generate hydrogen sulfide, which combines with ferrous ions or lead ions to form black precipitates
.
The hydrogen sulfide test is mainly used to identify Enterobacteriaceae bacteria

4.
Phenylalanine test bacteria can deaminate phenylalanine into phenylpyruvate, and keto acid can turn the iron trichloride indicator green
.
Proteus and Providencia have the activity of phenylalanine deaminase, and those who turn green are positive

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