IN-VITRO POSTANTIBIOTIC EFFECT OF SPARFLOXACIN AND CIPROFLOXACIN AGAINST PSEUDOMONAS-AERUGINOSA AND ENTEROCOCCUS-FAECALIS

The effect of concentration and exposure time on the postantibiotic ef fect (PAE) of sparfloxacin and ciprofloxacin against Pseudomonas aerug inosa Psa-1 and Entero-coccus faecalis SD-63 was evaluated by the colo ny counting method using centrifugation to remove the antibiotic. The microorganisms were exposed for 15, 30 and 60 min to drug concentratio ns ranging from 1 x MIC to 31 x MIC. The PAE was calculated as the dif ference in time required by test and control cultures to increase 1 lo g(10) after the drug was removed. The MICs of sparfloxacin for P. aeru ginosa and E. faecalis were 0.50 mg/L and 0.25 mg/L, respectively, whe reas 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 w as reached. On the contrary, against P. aeruginosa this point was reac hed at 8 x MIC of ciprofloxacin and 16 x MIC of sparfloxacin PAE value s of sparfloxacin for P. aeruginosa and E. faecalis ranged from 7 to 9 6 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. Significa nt PAEs for P. aeruginosa were obtained after 60 min exposure at 4 x M IC (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. Both quinolones showed longer PAEs against P. aeruginosa than against E. faecalis, except at concentrations above 8 x MIC of ci profloxacin and 16 x MIC of sparfloxacin where PAEs produced against E . faecalis were longer.