Modifications for disk diffusion susceptibility testing criteria of clinafloxacin (CI-960, AM-1091, PD127371) and fleroxacin (Ro 23-6240, AM-833) following studies with a challenge panel of ciprofloxacin-resistant clinical isolates.

R N Jones, D M Johnson

Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.

Diagnostic microbiology and infectious disease 1995 Apr

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A collection of ciprofloxacin-resistant organisms (200 strains) was developed among 300 total test strains to "challenge" the initial interpretive criteria developed for clinafloxacin (formerly CI-960), fleroxacin (formerly Ro 23-6240, AM-833), and ciprofloxacin. Generated results indicate the necessity for modified criteria for disk diffusion tests (5-micrograms disks) as follows: for clinafloxacin, susceptible at > or = 21 mm ( < or = 1 microgram/ml) and resistant at < or = 17 mm ( > or = 4 micrograms/ml), or susceptible at > or = 19 mm ( < or = 2 micrograms/liter) and resistant at < or = 15 mm ( > or = 8 micrograms/ml); for fleroxacin, susceptible at > or = 16 mm ( < or = 2 micrograms/ml) and resistant at < or = 11 mm ( > or = 8 micrograms/ml); and for ciprofloxacin, resistant at < or = 17 mm > or = 4 micrograms/ml). These modifications maximize total absolute interpretive accuracy between the standardized test methods, especially minimizing the potential for false susceptibility (very major errors) when testing truly resistant isolates. The clinafloxacin spectrum was widest against these resistant isolates, and the other two tested fluoroquinolones (ciprofloxacin, fleroxacin) possessed comparable overall spectrums of activity, although ciprofloxacin was generally more active on a weight basis. We urge the rapid acceptance of these criteria to improve the accuracy of the widely used National Committee for Clinical Laboratory Standards method for disk diffusion tests.

Citation

R N Jones, D M Johnson. Modifications for disk diffusion susceptibility testing criteria of clinafloxacin (CI-960, AM-1091, PD127371) and fleroxacin (Ro 23-6240, AM-833) following studies with a challenge panel of ciprofloxacin-resistant clinical isolates. Diagnostic microbiology and infectious disease. 1995 Apr;21(4):209-13