Reevaluations of disk diffusion susceptibility testing interpretive criteria for lomefloxacin and norfloxacin using fluoroquinolone-resistant isolates.
The current National Committee for Clinical Laboratory Standards interpretive criteria for disk diffusion susceptibility testing of lomefloxacin and norfloxacin were reevaluated using a test panel of 298 bacteria (200 with ciprofloxacin minimum inhibitory concentrations (MICs) at > or = 4 micrograms/ml). MICs were correlated with the diameter of zones of inhibition by regression statistics and error-rate bounding methods. Modifications of the interpretive criteria for lomefloxacin disk susceptibility testing are proposed as follows: susceptible at > or = 20 mm and resistant at < or = 16 mm, a 2-mm decrease of existing break-point zones. These criteria result in an absolute interpretive agreement of 95.3% with a very major (false susceptible) error rate of only 0.7%. The currently used criteria for norfloxacin (susceptible at > or = 16 mm and resistant at < or = 13 mm) were validated, and these break-points had an absolute interpretive correlation between methods of 91.9%. The change proposed for lomefloxacin disk interpretations would minimize minor and major errors most often reported for Staphylococcus saprophyticus isolates.
Cormican
M G
MG
Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.
Jones
R N
RN
D000890:Anti-Infective Agents / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D024841:Fluoroquinolones; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009643:Norfloxacin / Q000494:pharmacology*; D015363:Quinolones / Q000494:pharmacology*; D012680:Sensitivity and Specificity
D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D015363:Quinolones; C053091:lomefloxacin; D009643:Norfloxacin