🦠

Understanding the Kirby-Bauer Antibiotic Test

May 28, 2025

Antibiotic Sensitivity Testing: Kirby-Bauer Assay

Introduction

  • Purpose: Determine if a specific antibiotic can inhibit bacterial growth.
  • Method Used: Kirby-Bauer Antibiotic Sensitivity Assay.
  • Visual Aid: Use of food coloring to demonstrate antibiotic diffusion.

Materials Needed

  • Antibiotic discs (pre-soaked)
  • Petri dish
  • Gloves
  • Tweezers
  • Sterile cotton swabs
  • Marker
  • Container for waste
  • Plates with single colonies and blank plates

Experiment Steps

Preparation

  1. Gloves: Put on gloves for safety and contamination prevention.
  2. Labeling: Label the bottom of the plate with initials, date, etc.

Inoculation

  1. Use of Sterile Swab: Avoid contamination of the cotton tip.
    • Mark the swab for orientation.
  2. Pick Colony: Use the swab to pick a single bacterial colony.
  3. Create a Lawn: Spread bacteria evenly over the blank plate in two directions.
  4. Dispose: Discard the used swab in waste container.

Placing Antibiotic Discs

  1. Divide Plate: Into six sections for placement.
  2. Use Tweezers: Place each antibiotic disc in designated section.
    • Gently tap disc to fix it onto the agar.
    • Check disc labels for antibiotic type and concentration.
  3. Avoid Contamination: Use lid as a shield.
  4. Placement: If a disc falls, leave it in place.

Incubation

  1. Incubator Settings: 37° C for 24-48 hours or as directed.

Observations

  • Zones of Inhibition: Clear areas around discs indicating susceptibility.

Measuring Susceptibility

  • Measure Diameter: Clear zone diameter to assess susceptibility.
  • Consideration Factors:
    • Antibiotic concentration and effectiveness.
    • Reference table utilization for results interpretation.

Additional Points

  • Unexpected Results: Consider unexpected outcomes.
  • Penicillin Example: Historical context of antibiotic discovery.

Review of Experiment

  1. Create a Lawn: Bacteria spread on plate.
  2. Place Discs: Antibiotic discs added.
  3. Growth Observation: Measure inhibition zones.
  4. Use Reference Table: Determine susceptibility, resistance, or intermediate phenotype.

Conclusion

  • Objective Achieved: Determine bacterial susceptibility to various antibiotics using the Kirby-Bauer method.

Full transcript