[Comparative antibacterial activity of fleroxacin: selection frequencies and outer membrane proteins of resistant mutants].

The antibacterial activity of fleroxacin was evaluated in 427 gram-positive and gram-negative strains, all isolated recently from clinical specimens and compared to that of ofloxacin, ciprofloxacin and co-trimoxazole. The activity of fleroxacin resembled to that of ofloxacin; its excellent activity against Haemophilus influenzae on the one hand and its lack of activity against beta-hemolytic streptococci on the other hand have to be mentioned. Selection frequencies for resistant clones were evaluated for clinical E. coli and Serratia marcescens isolates and the quinolones. With respect to clinical E. coli and Serratia marcescens isolates selection frequencies ranged from 10(-7) to 10(-9) in the presence of 2-fold or 8-fold the MIC. The outer membrane proteins of E. coli and Serratia marcescens wild-type strains were compared with those of their quinolone-resistant mutants. No discrepancies could be observed in E. coli, whereas some of the resistant Serratia marcescens mutants exhibited an increased expression of 31 kdal protein linked with a decrease of a 37 kdal major outer membrane protein. As these alterations could not be observed in each of the resistant mutants, it cannot be decided at present whether such alterations may provide an explanation for the resistance observed.