A sensitive standardised micro-gel well diffusion assay for the determination of antimicrobial activity

We have developed a highly sensitive micro-gel well diffusion assay for the determination of antimicrobial activity. In essence, the normal radial dif fusion type assay was adapted to perform it in a microtiter plate. We compa red our micro-gel well diffusion assay to a radial diffusion assay and a mi crotiter broth dilution method, using gramicidin S as model antibiotic, and Micrococcus luteus as the indicator organism. The micro-gel well diffusion assay was as sensitive as the microtiter broth dilution method, and approx imately twice as sensitive as the radial diffusion method. Data analysis to calculate minimum inhibitory concentration, 50% microbial growth inhibitio n and maximum inhibitory concentration was refined by generating dose-respo nse curves with the software package Prism(R) 3.0 (Graphpad Software Inc.). The minimum inhibitory concentrations, determined by the three methods, we re significantly different (P < 0.001), highlighting the limitations involv ed in comparing data obtained from different methods. (C) 2000 Elsevier Sci ence B.V. All rights reserved.