[Must pefloxacin and norfloxacin be studied separately against bacteria isolated from urinary tract infections by the...

2113 bacterial strains were isolated from urinary tract infections in 1992 in 133 French pathology laboratories, 2069 strains were tested using the API-ATB method and the UR-14030 system including NFX and an additional test for PFX. Frequencies of susceptible (S), intermediate (I) and resistant (R) strains to PFX and NFX were respectively (%): 83.3; 8.6; 8.1 and 83.1; 9.5; 7; 4. Overall rate of concordance (C), SS, II and RR, between the two antibiotics reached 92.8, minor discrepancies (Dm), SI, IS, RI and IR, 6.3 and major discrepancies (DM), SR and RS, 0.9 (K = 0.82). For Enterobacteriaceae (n = 1830), frequencies of strains S, I and R were: 90.4; 5.9 and 3.7 with PFX and 90.4; 6.1 and 3.5 with NFX. Percentages of C, Dm and DM were 95.1; 4.4 and 0.5 respectively. The Lee test showed that results obtained with NFX and PFX were equivalent (p < 0.001) allowing to consider that the test of NFX is sufficient to conclude for susceptibility or resistance to both antibiotics using the API-ATB method and the UR-14030 system. Dm were probably related in some cases to a low level resistance mechanism and to the difference between the higher breakpoints (4 micrograms/ml for PFX and 8 micrograms/ml for NFX). DM might be due to artefacts related to the bacterial inoculum size or to the antibiotic concentration obtained in the cupules.