Prevention of urinary tract infection in rats with an indigenous Lactobacillus casei strain
International Journal of Antimicrobial Agents
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The objective of this study was to determine and compare the biofilm elimination concentrations (BEC: the concentration which reduced the viability of biofilm organisms by at least 99.9%) of ciprofloxacin and tobramycin for Pseudomonas aeruginosa, a common cause of nosocomial biomaterial-related infections. Bacterial biofilms were produced in the modified Robbins device using continuous culture flow at 60 ml/h for 40-44 h, and the sessile organisms were then exposed to either ciprofloxacin or tobramycin at a range of concentrations for 12 or 36 h. The BEC of ciprofloxacin was 5 μg/ml for the 12 and 36 h treatments, a value 10 x greater than the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). In contrast, the BEC of tobramycin was > 100 μg/ml after 12 h and 75 ug/ml following 36 h of drug exposure that is 75-100 x the MIC and MBC. The results demonstrated that the BEC is a more suitable indicator of the antibiotic susceptibility of P. aeruginosa biofilms than the MIC and MBC. Ciprofloxacin was significantly more effective than tobramycin in the treatment of P. aeruginosa 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.