The time-consuming nature of the broth dilution procedure led many laboratories in the United States to switch to disc diffusion tests in the early 1950s. Antibiotic susceptibility testing is done using Kirby Bauer assays, sometimes referred to as the Disc diffusion test. In the 1960s, there was an issue due to a lack of standardisation, and Kirby and Bauer later evaluated the description. WHO standardised the process in 1961. The original technique is currently updated and modified by CLSI, ensuring global uniformity. This test is mostly used to evaluate how susceptible or resistant aerobes or facultatively anaerobes are to various antibiotic classes.
Table of Contents
- Aim/ Objectives
- Principle of Kirby Bauer Disc Diffusion Method
- Materials Required
- Procedure of Kirby Bauer Disc Diffusion Method
- Result and Interpretation of Kirby Bauer Disc Diffusion Method
- Uses of Kirby Bauer Disc Diffusion Method
- Advantages
- Limitations
Aim/ Objectives
- This method assists medical professionals in making treatment decisions.
- The capacity of antibiotics to stop an organism depends on its rate of growth.
Principle of Kirby Bauer Disc Diffusion Method
The test organism must be cultured in broth for an entire night before being compared to the 0.5 McFarland Turbidity standard. Because it does not block sulphonamides and provides repeatability with the medium's composition and pH, Mueller-Hinton agar must be employed. When put onto Petri plates, the agar should be 4mm thick.
Materials Required
- Mueller- Hinton agar
- Antibiotic discs
- Cotton swabs
- Petri dishes
- 0.5 McFarland Turbidity standard
- Inoculum
- Forceps
- Metric ruler or caliper
Procedure of Kirby Bauer Disc Diffusion Method
- Before doing the test, sanitise the area and turn on the hob.
- To remove extra medium, a sterile cotton swab is dipped into the inoculum and pressed against the tube wall.
- Rotate the plate to fully swab its whole surface area. Lawn culture or carpet culture are two names for this method.
- For the medium to effectively absorb the inoculum, let the plates five minutes to dry.
- Before picking up antibiotic discs, first sanitise the forceps with alcohol.
- Discs ought to be spaced apart by 24 mm.
- To prevent misplacement, lightly touch each disc with the forceps to make sure it is in contact well.
- Turn the plate over and incubate it for 24 hours at 37 °C.
Result and Interpretation of Kirby Bauer Disc Diffusion Method
- Use a metric ruler to measure the zone of inhibition and factor in the diameter of the disc after the 24-hour incubation period.
- To report the outcome, compare it to the CLSI standards.
- Susceptible (S), Intermediate (I), or Resistant (R) are the results' respective designations.
Uses of Kirby Bauer Disc Diffusion Method
- Testing for antibiotic susceptibility is a crucial step in keeping track of antimicrobial resistance.
- It helps the practitioner decide which antimicrobial agent is best.
- to gather knowledge on important bacteria for public health.
Advantages
- The results of this test are used to choose the best medications to treat an illness.
- It can be helpful for choosing the right antibacterial agents and for monitoring antimicrobials.
- It may be performed without specific equipment and is interpretable by all medical staff.
- This test is less expensive to run.
Limitations
- Not all slow or exacting creatures can be correctly examined.
- According to the CLSI recommendation, it is only used to screen the susceptibility pattern of the organisms, hence it cannot be regarded as the gold standard test.
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