Correlation of netilmicin agar dilution and disk diffusion susceptibilities.

A study of 283 isolates of gram-negative bacilli revealed a good correlation (r = -0.74) between disk diffusion zones of inhibition and agar dilution minimal inhibitory concentrations. Regression analysis suggested that strains with zone sizes =/<11 mm should be considered resistant, but 34 of 45 strains resistant by minimal inhibitory concentration (including 27 strains of Pseudomonas aeruginosa) would have been called susceptible using this break point.