Interpretive criteria for CI-960 (AM-1091, PD127391) disk diffusion tests using 5-microgram disks

CI-960, a new potent fluoroquinolone, was evaluated to develop disk diffusion susceptibility criteria for a 5-micrograms content disk. Preliminary interpretive zone diameter criteria were proposed for two possible susceptible breakpoint MICs (less than or equal to 1 and less than or equal to 2 micrograms/ml). Both sets of interpretive criteria performed well having 96.8%-98.4% absolute agreement and no false-susceptible errors. The more conservative less than or equal to 1-microgram/ml breakpoint criteria had correlate zones of greater than or equal to 23 mm for susceptible and less than or equal to 19 mm for resistant. These criteria produced no false resistance, whereas 0.7% of strains exhibited major errors at the less than or equal to 2-micrograms/ml breakpoint.