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Principle
- Agrinine dihydrolase broth is composed of peptone, L-arginine, Dipotassium phosphate, sodium chloride, bromo cresol purple, and agar.
- Peptone provides nitrogen and essential nutrients. L-arginine is a substrate for arginine dihydrolase. Dipotassium phosphate buffers the medium. Sodium chloride maintains osmatic equilibrium. Bromocresol purple is a pH indicator dye.
- Agar is the solidifying agent. The dextrose fermentation produce acid decreases the pH of the medium and changes the indicator from purple to yellow. If the bacteria produce the arginine dihydrolase or decarboxylase, produce amines, resulting in an increase in the pH of the medium causing the indicator to change from yellow to light or deep purple.
- For Enterobacteriaceae differentiation, a control tube is used without arginine. If the control tubes give positive purple reaction the test is considered as negative.
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