Biochemical Tests and Dilution Calculations

Flashcards to help review critical biochemical test results and dilution calculations for the exam.

What indicates a positive starch test for amylase?

A clear zone around bacterial growth after addition of iodine.

What does the neutral red pH indicator indicate in fat agar plates?

It turns red with the presence of acidity due to fatty acids.

What is the product of the gelatinase enzyme?

Amino acids.

What result indicates the presence of hydrogen sulfide in the hydrogen sulfide test?

Black precipitate.

What indicates a positive urease test?

Fuchsia color in the medium.

What is the product produced in the citric acid test?

Ammonia (NH₃) or ammonium hydroxide (NH₄OH).

What represents a positive result for the Indole test?

Red color after adding Kovac’s reagent.

What is the formula for calculating dilution?

Dilution = part ÷ whole.

What is the effective dilution of a 10⁻² tube when plated?

Effective dilution = dilution × 0.1 mL.

What range of colonies per plate is considered countable?

30 to 300 colonies.