6.2: Kirby Bauer Procedure
Kirby Bauer Test
Name: _____________________________________________________
Course Section: ______________________________________________
The following activity will teach students how to perform a Kirby Bauer antibiotic susceptibility test. Post-inoculation, students will determine the antibiotic susceptibility of a given bacterial species.
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Day 2:
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Figure 1. Zones of inhibition are measured in millimeters (mm).
Results
| Antibiotic disk abbreviation | Antibiotic name | Antibiotic disk concentration | Resistant (mm) | Intermediate (mm) | Susceptible (mm) |
| E15 | Erythromycin | 15 µg | 13 or less | 14 – 22 | 23 or more |
| CIP5 | Ciprofloxacin | 5µg | 15 or less | 16 - 20 | 21 or more |
| SXT | Trimethoprim | 1.25µg | 10 or less | 11 - 15 | 16 or more |
| P10 |
Penicillin ( Staphylococcus) |
10 U | 28 or less | 29 or more | |
| P10 |
Penicillin (other bacteria) |
10 U | 14 or less | 15 or more | |
| C30 | Chloramphenicol | 30 µg | 12 or less | 13 – 17 | 18 or more |
| TE30 | Tetracycline | 30 µg | 14 or less | 15 – 18 | 19 or more |
| Antibiotic disk | Diameter of the zone of inhibition (mm) | ____________________ is... (resistant, intermediate, or susceptible) to this antibiotic. |
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Complete the table above using measurements of the diameter of the zones of inhibition and the interpretation table above to determine if your bacteria are resistant, intermediate, or susceptible to each antibiotic.
General Questions
1. If you had a patient with an infection of this strain, which antibiotic(s) might be a good choice for treatment? Explain your answer.
2. Define "zone of inhibition."
3. Explain how the size of the zone of inhibition relates to the concentration of the antibiotic.
4. Explain how the size of the zone of inhibition relates to the susceptibility or resistance to an antibiotic.
5. Define antibiotic resistance?
6. Why do physicians often rely on empirical evidence rather than waiting for susceptibility testing when prescribing antibiotics?
7. What risks are associated with selecting an inappropriate empiric therapy, both for the patient and in terms of promoting antimicrobial resistance?