Overview
The Kirby–Bauer method is the standardized disk diffusion procedure that combines controlled inoculum, Mueller–Hinton agar, defined disks, incubation, and zone measurement for interpretive category assignment under adopted breakpoints.
Classification
| Step | Must verify | Reject if |
|---|---|---|
| Growth source | Fresh, pure colonies | Aged/mixed inoculum |
| Density | McFarland match | Eye-ball only |
| Lawn | Confluent uniform | Patchy/sparse |
| QC | Documented in range | Unread or out |
Morphologic Features
Zones should be round and measurable. Fuzzy edges, swarming, or inner colonies: apply organism-/agent-specific SOP reading rules.
Laboratory Characteristics
- Calibrated turbidity standard or device
- Three-direction swab pattern (typical)
- Disk dispenser or forceps with asepsis
- Inverted incubation per method
- Millimeter measurement discipline
Reference Intervals
QC zone charts and clinical breakpoints are institutional, verify the laboratory’s CLSI or EUCAST edition and local medium/disk lot acceptances.
Clinical and Laboratory Significance
Properly controlled Kirby–Bauer provides reportable categories for validated organism–agent pairs. Procedural failures require repeat, not estimation.
Differential Considerations
Differentiate resistance-related small zones from heavy inoculum, delayed disks, degraded disks, incorrect agar, and measurement bias.
Comparison Tables
Kirby–Bauer procedure traps
| Trainee shortcut | Likely effect | Corrective action |
|---|---|---|
| No McFarland standard | Unpredictable zones | Remake inoculum to density |
| Long delay before disks | Distorted zones | Repeat within time window |
| QC unread | Unknown method status | Read QC; hold patients |
Classification Frameworks
Not applicable.
Laboratory Notes
- No drug selection or dosing commentary
- Hedge breakpoints and QC ranges as institutional
- Inoculum, media, reading, QC define the method
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
Common questions about using this Kirby-Bauer Method foundational topics Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Kirby-Bauer Method laboratory reference?
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