The arginine dihydrolase test (ADH test) is a biochemical test used primarily to determine which bacteria can produce the enzyme arginine dihydrolase. This enzyme breaks down the amino acid arginine through a process called dihydrolysis.
Arginine dihydrolase enzyme converts arginine into ornithine, ammonia, and carbon dioxide. This reaction causes a change in pH, which is detected by a pH indicator in the test medium.
Arginine dihydrolase test procedure
- A broth or semi-solid medium containing arginine and a pH indicator (phenol red) is inoculated with the test organism.
- The inoculated medium is typically incubated for 24-48 hours at an appropriate temperature (usually 35-37°C).
- After incubation, the color change in the medium is observed.
- A color shift to purple (alkaline pH), indicating the presence of arginine dihydrolase in positive result.
- No color change or a shift to yellow (acidic pH), indicating the absence of enzyme activity and negative result.
Result Interpretation
- A color shift to purple : The organism can hydrolyze arginine, indicating that it possesses the arginine dihydrolase enzyme.
- No color change : The organism cannot hydrolyze arginine, indicating a lack of arginine dihydrolase enzyme.
Uses of Arginine dihydrolase test
The arginine dihydrolase test is one among many tests used for:
- Differentiating members of Enterobacteriaceae and Pseudomonas.
- Identifying other Gram-negative and some Gram-positive bacteria.