Physiological Characteristics: Oxidative/Fermentative

Exercise 39 Objectives

  • The exercise aims to understand physiological tests used to differentiate bacteria based on their metabolic processes.   - For each physiological test, students are required to list:     - AKA (also known as)
        - Media used in the test
        - Enzyme involved in the metabolic process
        - (+) Control m/o (microorganism) that demonstrates a positive result
        - Reagent used in the test
        - (+) Result indicating a positive outcome

  • Interpret positive and negative results for each test.

  • Name tests included in IMViC (Indole, Methyl Red, Voges-Proskauer, Citrate utilization).

  • Know IMViC results for Escherichia coli and Enterobacter aerogenes.

Exercise 39: Oxidative/Fermentative

  • Overview of oxidative and fermentative reactions is critical for understanding metabolic pathways in bacteria.

  • Control microorganisms:
      - Escherichia coli
      - Enterobacter aerogenes

A. Sugar Fermentation

  • AKA: n/a

  • Media: Phenol red "sugar" broth

  • Enzyme: Varies depending on the specific sugar

  • Control m/o: Escherichia coli in glucose

  • Reagent: n/a

  • (+) Result:
      - Acid production indicated by yellow color change
      - Gas production indicated by bubbles in the Durham tube

Results Interpretation

  • Positive carbohydrate fermentation:
      - Demonstrates fermentation and gas production

  • Negative carbohydrate fermentation:
      - No acid or gas production is observed

B. Mixed Acid Fermentation

  • AKA: Methyl red test

  • Media: MR-VP (Methyl Red - Voges-Proskauer medium)

  • Enzyme: Formic hydrogenylase

  • Control m/o: Escherichia coli

  • Reagent: Methyl red

  • (+) Result: Red color is produced, indicating acid production

C. Butanediol Fermentation

  • AKA: Voges-Proskauer test

  • Media: MR-VP

  • Enzyme: n/a

  • Control m/o: Enterobacter aerogenes

  • Reagent: Barritt’s reagents A and B (alpha naphthol and KOH)

  • (+) Result: Red color develops upon aeration, indicating butanediol production

D. Nitrate Reduction

  • AKA: n/a

  • Media: Nitrate broth

  • Enzyme: Nitratase (nitrate reductase)

  • Control m/o: Escherichia coli

  • Reagent: Nitrite test reagents

  • (+) Result: Red color development, which may fade over time

IMViC Tests

  • IMViC stands for a series of tests used to identify groups of Enterobacteriaceae:   - I: Indole (tryptophan hydrolysis)
      - M: Methyl Red (mixed acid fermentation)
      - V(i): Voges-Proskauer (butanediol fermentation)
      - C: Citrate utilization

IMViC Results for Specific Genera of Bacteria

  • IMVIC Reactions for various bacteria:   

  • Escherichia:
        - I: +
        - M: +
        - V: -
        - C: -
      - Enterobacter:
        - I: -
        - M: -
        - V: +
        - C: +