Regression analysis, proposed interpretative zone size standards, and quality control guidelines for a new macrolide antimicrobial agent, A-56268 (TE-031)

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Abstract
A-56268 is a 6-0-methyl derivative of erythromycin A which has a spectrum of activity similar to that of erythromycin and is 1 log2 dilution more potent than erythromycin against most organisms that have been tested. The correlation of zone size diameters and MICs of A-56268 for 461 strains of bacteria isolated from clinical specimens was investigated. Based on anticipated levels in human serum of 2 .mu.g/ml, 15-.mu.g disks have been recommended with zone size standards of .gtoreq. 15 mm for susceptibility (MIC correlate, .ltoreq. 2.0 .mu.g/ml) and .ltoreq. 11 mm for resistance (MIC correlate, .gtoreq. 8 .mu.g/ml). Selection of these tentative breakpoints resulted in no very major errors (false susceptible), a major error (false resistant) rate of 0.22%, and an acceptable minor error (intermediate) rate of 2.82%. MIC ranges and zone diameter limits for quality control organisms used in the standardized agar dilution and disk diffusion susceptibility tests with A-56268 are given.