PROPOSED CRITERIA FOR INTERPRETATION OF SUSCEPTIBILITIES OF STRAINS OF NEISSERIA-GONORRHOEAE TO CIPROFLOXACIN, OFLOXACIN, ENOXACIN, LOMEFLOXACIN, AND NORFLOXACIN

The susceptibilities of 45 strains of Neisseria gonorrhoeae, including 25 strains susceptible to ciprofloxacin (MICs, less than or equal to 0.06 mu g/ml) and 20 strains exhibiting decreased susceptibilities to ciprofloxacin (MICs, greater than or equal to 0.125 mu g/ml), to cipro floxacin, ofloxacin, enoxacin, lomefloxacin, norfloxacin, and nalidixi c acid were determined by agar dilution and disk diffusion. On the bas is of theoretical calculations of predicted susceptibilities at which infections may fail therapy (supported by observed failures of infecti ons to respond to the therapeutic doses of enoxacin and ciprofloxacin) , the Centers for Disease Control and Prevention has adopted the follo wing agar dilution breakpoints for interpretation of resistance to the se agents: MICs of greater than or equal to 1.0 mu g of ciprofloxacin, enoxacin, and norfloxacin per ml and MICs of greater than or equal to 2.0 mu g of ofloxacin and lomefloxacin per ml. The corresponding disk diffusion breakpoints for these agents were as follows: ciprofloxacin , less than or equal to 29 mm; ofloxacin, less than or equal to 24 mm; enoxacin, less than or equal to 31 mm; lomefloxacin, less than or equ al to 26 mm; and norfloxacin, less than or equal to 32 mm. The Centers for Disease Control and Prevention recommends two strains as interim quality control strains for susceptibility testing of ciprofloxacin an d ofloxacin. These are N.gonorrhoeae CDC-10,328 (MIC of ciprofloxacin, 0.125 to 0.25 mu g/ml [inhibition zone diameter range, 30 to 34 mm]; MIC of ofloxacin, 0.5 mu g/ml [inhibition zone diameter range, 27 to 3 2 mm]) and N.gonorrhoeae CDC-10,329 (MIC of ciprofloxacin, 1.0 to 2.0 mu g/ml [zone inhibition diameter range, 21 to 26mm]; MIC of ofloxacin 2.0 mu g/ml [inhibition zone diameter range, 18 to 21 mm]).