Microbial Identification Biochemical Tests: Your Ultimate Study Guide
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29 cards
Question: What enzyme and indicator are used to test for starch hydrolysis, and what indicates a positive result?
Answer: Enzyme: amylase; Indicator: iodine. Positive: clear zone around growth (black/golden with iodine otherwise).
Question: What substrate and enzyme are involved in gelatin hydrolysis and how is a positive test identified?
Answer: Substrate: gelatin; Enzyme: gelatinase. Positive: liquid after cooling (gelatin remains liquid). Negative: solidifies after refrigeration.
Question: In phenol red carbohydrate fermentation broths, what indicates fermentation with acid and possibly gas?
Answer: Indicator: phenol red. Positive fermentation: yellow color; gas indicated by bubble in Durham tube.
Question: How does litmus milk show acid (lactic acid) fermentation and what are the appearance changes?
Answer: Fermentation produces lactic acid and ATP; litmus turns pink with milk becoming purple milk and may show 'organic' lactic acid changes (pink).
Question: What does alkalinization of litmus milk indicate and what is the appearance?
Answer: Proteolysis or casein breakdown producing basic products; appearance: purple/blue (alkaline) or magenta/red depending on context.
Question: What indicates peptonization in litmus milk and what appearance results?
Answer: Protease activity breaking down casein to polypeptides/amino acids; appearance: clear or brown, purple/blue to pink depending on reaction.
Question: How is reduction detected in litmus milk and what visual change occurs?
Answer: Reduction (loss of oxygen) reduces litmus and may bleach it; appearance: reduced litmus becomes white/bleached from purple.
Question: Which reagents are used to detect nitrate reduction and what result indicates nitrate reduction to nitrite or N2 gas?
Answer: Reagents: 2 drops of DAN and 3 drops of SA (as listed). Positive: red after reagents or magenta/baby pink indicating nitrite or N2 gas.
Question: What does a positive decarboxylase broth test show and what enzyme/pathway is involved?
Answer: Substrate: amino acid; Enzyme: decarboxylase producing basic amine (alkaline). Positive: color change to purple/burgundy (alkaline).
Question: What enzyme hydrolyzes urea and what indicates a positive urease test?
Answer: Enzyme: urease. Urea hydrolysis yields ammonia and CO2 making medium basic; positive: bright pink. Negative: yellow/orange.