Biochemical Tests

Citrate Utilization Test

tests microorganisms ability to use citrate as its sole source of carbon and energy, uses bromothymol blue as pH indicator

positive result - color will change from green to blue

TSI Test

detects organisms that ferment different types of sugars, detects bacteria that degrade amino acid and produce H₂S gas (black precipitate)

• slant/deep allows for aerobic + anaerobic growth conditions

MR-VP Tests

Methyl Red-Vogues Proskauer Test; test acidic and neutral pathway of glucose

red - positive MR

Pink - positive VP

Urease Test

agar contains urea & phenol red

• when urease is present, it will convert urea to CO₂ and NH₃

• ammonia + water will create strong base, increasing pH and phenol red will turn deep pink

SIM Test

multi-test medium for production of hydrogen sulfide, formation of indole, and motility

• hydrogen sulfide produced - black

• indole: some microorganisms can metabolize tryptophan by tryptophanase

  • leads to formation of pyruvic acid, indole, and ammonia

• motile? based on how far bacteria spreads from stab

Nitrate Reductase Test