In-vitro postantibiotic effect of sparfloxacin and ciprofloxacin against Pseudomonas aeruginosa and Enterococcus faecalis.

The effect of concentration and exposure time on the postantibiotic effect (PAE) of sparfloxacin and ciprofloxacin against Pseudomonas aeruginosa Psa-1 and Enterococcus faecalis SD-63 was evaluated by the colony counting method using centrifugation to remove the antibiotic. The microorganisms were exposed for 15, 30 and 60 min to drug concentrations ranging from 1 x MIC to 31 x MIC. The PAE was calculated as the difference in time required by test and control cultures to increase 1 log10 after the drug was removed. The MICs of sparfloxacin for P. aeruginosa and E. faecalis were 0.50 mg/L and 0.25 mg/L, respectively, whereas the MICs of ciprofloxacin were 0.25 mg/L for P. aeruginosa and 0.50 mg/L for E. faecalis. PAEs increased as a function of concentration and exposure time. Against E. faecalis no point of maximal response was reached. On the contrary, against P. aeruginosa this point was reached at 8 x MIC of ciprofloxacin and 16 x MIC of sparfloxacin PAE values of sparfloxacin for P. aeruginosa and E. faecalis ranged from 7 to 96 min and from 0 to 112 min, respectively, and those of ciprofloxacin from 8.5 to 82.33 min and from 0 to > 136 min, respectively. Significant PAEs for P. aeruginosa were obtained after 60 min exposure at 4 x MIC (62.6 min) and 2 x MIC (52.6 min) of ciprofloxacin and sparfloxacin, respectively, and at 8 x MIC (81.5 min) and 16 x MIC (81.6 min) for E. faecalis.(ABSTRACT TRUNCATED AT 250 WORDS)