[Antibacterial activity of norfloxacin, ofloxacin and ciprofloxacin according to resistance phenotypes to nalidixic acid and pefloxacin].

In vitro antibacterial activity of 5 quinolones: nalidixic acid (NAL), pefloxacin (PEF), norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP) was evaluated by agar diffusion (disks Diagnostics Pasteur) for 1,253 bacterial strains (767 Enterobacteriaceae: E 164 P. aeruginosa: PA, 90 A. baumannii: AB and 232 S. aureus: SA) isolated during the last three months of 1988. Strains were ranged in susceptible (S) intermediate (I) and resistant (R) according to recommendations of Comité Français de l'Antibiogramme; in addition, activity of NOR, OFL and CIP was precised according to susceptibility to NAL and PEF. Frequencies of strains R + I observed for NAL, PEF, NOR, OFL and CIP were (%): E: 14.4; 13.4; 7.3; 7.6; 2.4 - PA: 100; 68.5; 18.4; 36.8; 8.9 - AB: 78.9; 57.8; 75.5; 54.4; 50 - SA: 100; 27.5; 28.9; 28.5; 28.7. For E and AB, analysis according to resistance phenotypes to NAL and PEF showed reduction of activity of NOR, OFL and CIP, on strains RI and particularly RR by comparison with strains SS and RS. Activity of PEF, NOR, OFL and CIP is similar on PA, belonging to RS and RR phenotypes. On RI strains, only CIP showed activity practically identical to that on RS strains. For SA, NOR, OFL and CIP were inactive on PEF R strains. Analysis of populations of strains according to resistance phenotypes to NAL and PEF permitted to show reduction of activity of other compounds on strains with an acquired resistance character to quinolones; currently, only test of PEF is presently sufficient for susceptibility testing of other fluoroquinolones (NOR, OFL and CIP) on E, AB and SA; however for PA, test of CIP is also necessary.