SUGGESTED MODIFICATIONS FOR DISK DIFFUSION SUSCEPTIBILITY TESTING CRITERIA FOR LEVOFLOXACIN AND SPARFLOXACIN FOLLOWING TESTS WITH A PREDICTOR PANEL OF CIPROFLOXACIN-RESISTANT CLINICAL ISOLATES

A predictor panel of 300 clinical bacterial isolates (200 resistant to ciprofloxacin) was used to compare 5-mu g disk diffusion test results with the MICs of ofloxacin (control), levofloxacin, and sparfloxacin, Regression analysis demonstrated high correlations between the methods for all three fluoroquinolones (r greater than or equal to 0.95), In order to minimize disk diffusion testing errors among the fluoroquinolone-resistant strains, the following modifications to previously proposed or published interpretive criteria were. suggested: for levofloxacin, susceptible at greater than or equal to 17 mm (less than or equal to 2 mu g/ml) and resistant at less than or equal to 13 mm (greater than or equal to 8 mu g/ml); for sparfloxacin, susceptible at greater than or equal to 20 mm (less than or equal to 1 mu g/ml) and resistant at less than or equal to 16 mm (greater than or equal to 4 mu g/ml), The study control drug, ofloxacin, did not appear to possess a significant error rate (5% minor error) when fluoroquinolone-resistant strains were tested, and no modifications were proposed, Under these proposed interpretive criteria, the absolute categorical agreements between standardized susceptibility testing methods for levofloxacin and sparfloxacin results were 91.3 and 94.0%, respectively (less than or equal to 0.3% major errors and nil very major errors),