Evaluation of post-antibiotic effects of antipseudomonal antibiotics using an automated system

Different methods have been described for determination of the post-antibiotic effects (PAEs) of antibiotics, from the conventional methods to the automatic measurement of bacterial regrowth. The PAEs of ciprofloxacin, ofloxacin and perfloxacin, as compared with those of amikacin, netilmicin and ceftazidime, have now been investigated for three clinical isolates of Pseudomonas species, using automated measurement of the growth with an Anthos microplate reader. It was found that, besides the well-known PAEs of aminoglycosides, quinolone antibiotics also exhibit drug- and concentration-dependent PAEs against clinical isolates of Pseudomonas when used in concentrations of 1/2x, 1 x or 5 x MIC. Of the three quinolones tested, pefloxacin showed the greatest PAE, independently of its MICs against the different strains. Ofloxacin had no or only an insignificant PAE, while ciprofloxacin had a marked PAE for all strains, including the reference strains.