Biochemical Identification of Bacteria

Commonly Used Tests

1. Catalase Test

   • Used in the case of all bacteria.
   • Mixing a bacterial colony with hydrogen peroxide produces O2.
   • Positive Example: Staphylococcus species
   • Negative Example: Rajobacter and Serpens

2. Oxidase Test

   • Identifies cytochrome oxidase enzyme.
   • Bacterial colony smear with oxidase reagent turns deep purple.
   • Positive Example: Pseudomonas, Vibrio, Bacillus
   • Negative Example: Enterobacteria, Acinetobacter

Tests for Gram-Negative Bacilli

1. Indole Test

   • Identifies the enzyme tryptophanase.
   • Positive Example: E.coli, Vibrio cholerae
   • Negative Example: Klebsiella pneumoniae

2. Citrate Utilization Test

   • Identifies bacteria that use citrate as a carbon source.
   • Positive Example: Klebsiella pneumoniae, Citrobacter
   • Negative Example: E. coli, Shigella

3. Urea Hydrolysis Test

   • Checks for urease enzyme-producing bacteria.
   • Positive Example: Proteus vulgaris

4. Triple Sugar Iron Test (TSI)

   • Checks for acid and gas production.
   • Example: E.coli (acid-producing), Salmonella (H2S-producing)

Further Discussion

• The next video will discuss tests for gram-positive bacteria.

These notes provide a summary of important points for the biochemical identification of bacteria and will serve as helpful study material for students.