[In vitro antibacterial activity of a new fluoroquinolone, fleroxacin as a function of the sensitivity or resistance to nalidixic acid and to pefloxacin].

Minimal inhibitory concentrations (MIC) of fleroxacin (FLE) were evaluated by agar dilution for 375 bacterial strains. For Enterobacteriaceae, MIC of FLE were (microgram/ml): nalidixic acid (NAL), susceptible (S), pefloxacin (PEF), susceptible (S) strains: 0.032 to 0.5; NAL, resistant (R), PEF S: 0.25 to 1; NAL R, PEF R: 1 to 32; NAL R, PEF R strains were particularly observed among Serratia marcescens and Providencia stuartii, Pseudomonas aeruginosa was less susceptible to FLE (MIC 1 to 4), as to PEF; two PEF R strains were inhibited by 32 micrograms/ml of FLE. FLE was active on A. baumannii PEF S strains (0.5), but this activity was reduced on PEF R strains (2 to 64). H. influenzae and N. meningitidis (0.03 to 0.06), N. gonorrhoeae (0.016 to 0.03) and L. pneumophila (0.03 to 0.25) were very susceptible to FLE. MIC of FLE on S. aureus were 0.25 to 1 for PEF S strains and greater than or equal to 16 for PEF R strains, also resistant to methicillin. Enterococci, Streptococci and Pneumococci were less susceptible to FLE (2 to 8). C. perfringens (0.5 to 1) appeared susceptible to FLE whereas B. fragilis was inhibited by higher concentrations (4 to 8). So, antibacterial properties of FLE are very similar to that of PEF; PEF R strains appear generally resistant to FLE.