[Comparison of the in vitro activity of 6 quinolones on Pseudomonas sp].

Activity of six quinolones (nalidixic acid, pipemidic acid, oxolinic acid, pefloxacin, ofloxacin and norfloxacin) against one-hundred and ten Pseudomonas strains was studied in vitro. Five species of Pseudomonas were represented, i.e. aeruginosa, maltophilia, cepacia, stutzeri and paucimobilis. Isolates came from two Paris hospitals. Minimal inhibitory concentrations (MICs) were determined using gelose dilution according to WHO recommendations (Mueller Hinton medium, multiple inoculator, controlled inoculum). Modal CMIs classify activities of the six tested quinolones against P. aeruginosa in the following order: nalidixic acid: 64 mg/l; pipemidic acid: 16-32 mg/l; oxolinic acid: 16 mg/l; pefloxacin: 2 mg/l; ofloxacin: 2 mg/l; norfloxacin: 1 mg/l. The other Pseudomonas species exhibit a variety of resistance phenotypes which are described in detail. High CMIs are found for certain P. aeruginosa strains. Two of these, i.e. DL 55 and DL 59, are highly resistant to all the tested quinolones. Their pattern of resistance is comparable to that of a mutant, PAO 38-02, obtained in vitro in the presence of pefloxacin. This fact suggests that quinolones may induce in vivo selection of resistant P. aeruginosa mutants.