Regression analyses for cefoperazone on Mueller-Hinton agar and DST agar.

A total of 142 gram-positive and 161 gram-negative bacterial strains were tested by an agar diffusion method using antibiotic disks (30 microgram/ml) and the broth dilution method in order to establish a relationship between zone diameter and minimal inhibitory concentration. Mueller-Hinton and DST-Oxoid agars were both evaluated to assess their effects on zone diameters. Computer programmed regression lines of the first and second order were determined, as well as the correlation coefficient of both regression lines. Acceptable correlation coefficients (R = 0.84-0.92) were achieved. The regression lines of the first and second order showed differences, which fell into the category of resistant/susceptible. The DST agar appeared to be better suited than the Mueller-Hinton agar (using the Bauer-Kirby method of the agar diffusion test) to show the differences in the breakpoints.