Interpretive criteria for DU-6859a disk diffusion tests using 5-μg disks

Abstract

In vitro disk diffusion test interpretive criteria were developed for DU-6859a, a new difluorinated quinolone, using a 5-micrograms disk. Included in the 494 organisms tested were 84 (17%) ciprofloxacin-resistant > or = 4 micrograms/ml) clinical isolates. The following interpretive criteria were proposed for two possible susceptible breakpoint minimum inhibitory concentrations: > or = 16 mm (< or = 2 micrograms/ml) = susceptible and < or = 12 mm (> or = 8 micrograms/ml) = resistant and; > or = 19 mm (< or = 1 microgram/ml) = susceptible and < or = 15 mm (> or = 4 micrograms/ml) = resistant. These criteria demonstrated > or = 97% absolute interpretive agreement between test methods with no major (false resistant) or very major (false susceptible) errors.