PSEUDOMONAS-AERUGINOSA BIOFILMS ARE MORE SUSCEPTIBLE TO CIPROFLOXACINTHAN TO TOBRAMYCIN

The objective of this study was to determine and compare the biofilm e limination concentrations (BEG: the concentration which reduced the vi ability of biofilm organisms by at least 99.9%) of ciprofloxacin and t obramycin for Pseudomonas aeruginosa, a common cause of nosocomial bio material-related infections. Bacterial biofilms were produced in the m odified Bobbins device using continuous culture flow at 60 ml/h for 40 -44 h, and the sessile organisms were then exposed to either ciproflox acin or tobramycin at a range of concentrations for 12 or 36h. The BEC of ciprofloxacin was 5 mu g/ml for the 12 and 36 h treatments, a valu e 10 x greater than the minimum inhibitory concentration (MIC) and min imum bactericidal concentration (MBC). In contrast, the BEC of tobramy cin was >100 mu g/ml after 12h and 75 mu g/ml following 36 h of drug e xposure, that is 75-100 x the MIC and MBC. The results demonstrated th at the BEC is a more suitable indicator of the antibiotic susceptibili ty of P. aeruginosa biofilms than the MIC and MBC. Ciprofloxacin was s ignificantly more effective than tqbramycin in the treatment of P. aer uginosa adherent to biomaterials. With respect to clinical application , if the intention of antibiotic use is to eradicate bacteria adherent to devices, only biofilm-active agents should be used. Copyright (C) 1996 Elsevier Science B.V.