Description For use with the Disc Diffusion Susceptibility Test SUMMARY AND EXPLANATION The Kirby-Bauer procedure is used for the determination of antimicrobial susceptibility based on the agar gel disc diffusion principle and measurement of the zone(s) of inhibition. Mueller Hinton agar is the medium of choice and a liquefied inoculum is required for uniform coverage of the plate and proper interpretation. The Kirby Bauer method utilizes breakpoints published as a consensus standard by the Clinical Laboratory Standards Institute (CLSI) and is periodically reviewed and updated. The inoculum concentration expressed as CFU/ml has been shown to be an important factor in obtaining valid results with the Kirby-Bauer procedure. The classical Kirby-Bauer procedure employed a bacterial suspension prepared from live cultures with an approximate concentration of 1 X 108 CFU/ml. Preparation required incubation in broth for 1-2 hours to achieve the desired inoculum concentration visually equivalent to the 0.5 McFarland turbidity standard. Several studies have subsequently shown that direct standardization of the inoculum, i.e., without incubation, is an acceptable alternative for routine testing purposes. The direct standardization method should only be used for rapidly growing bacteria such as Enterobacteriacae, Staphylococcus spp., Pseudomonas aeruginosa, Acinetobacter spp., enterococci, and some non-enterococcal Streptococci. PRODUCT DESCRIPTION This modification of the direct standardization procedure utilizes the Prompt® System-D inoculation wand and individual plastic tubes each containing 1 ml. of sterile saline and sealed with a leakproof cap. The polypropylene wand features a breakaway collar that serves as a wiping mechanism. The rod is attached to a stopper that for this procedure serves as a handle. At the tip of the wand is a groove designed to hold a specific number of bacteria (CFU). When used as directed, this method should achieve the recommended inoculum concentration of 1.08 to 1.58 CFU/ml.
