Disk diffusion susceptibility testing and broth microdilution quality control guidelines for BMY-28100, a new orally administered cephalosporin

Abstract

The BMY-28100 30-micrograms-disk test was evaluated by using 615 clinical isolates. Regression analyses and error rates were determined, leading to the recommendation of greater than or equal to 18-mm zone diameters (MIC correlate, greater than or equal to 8.0 micrograms/ml) for susceptibility and less than or equal to 14-mm zone diameters (MIC correlate, greater than or equal to 32 micrograms/ml) for resistance. Nearly all false-susceptible disk test results were among the Providencia spp. and the beta-lactamase-positive Haemophilus influenzae strains. Susceptibility disk test results for these species should be interpreted with caution. The following broth microdilution MIC quality control guidelines were determined from results of a multilaboratory trial: Escherichia coli ATCC 25922, 1.0 to 4.0 micrograms/ml; Enterococcus faecalis ATCC 29212, 4.0 to 16 micrograms/ml; Staphylococcus aureus ATCC 29213, 0.25 to 1.0 microgram/ml; and Pseudomonas aeruginosa ATCC 27853, greater than 32 micrograms/ml.