Prevention of Pseudomonas aeruginosa biofilm formation with antibiotics used in cystic fibrosis patients during early broncopulmonary colonisation

Abstract number: 1733_121

Fernandez-Olmos A., García-Castillo M., Maiz L., Lamas A., Baquero F., Cantón R.

Objectives: Early P. aeruginosa isolates colonising cystic fibrosis (CF) airway appear more favourable for eradication with antibiotic therapy than those in chronically colonised patients. We study the antibiotic susceptibilities of non-mucoid P. aeruginosa isolates recovered in early colonisation stages of CF patients and their ability to prevent biofilm formation in these isolates.

Methods: Ciprofloxacin (CIP), tobramycin (TOB), ceftazidime (CAZ) and imipenem (IMP) susceptibility of 27 non-mucoid P. aeruginosa isolates recovered from 18 CF patients with early colonisation were study both using a polystyrene microplate biofilm susceptibility assay (Moskowitz et al. J Clin Microbiol 2004; 42:1915–22) and the standard microdilution method (CLSI). Biofilm was formed by immersing the pegs of a modified microtiter lid into a growth microplate, followed by incubation. Biofilm inhibitory concentration (BIC) was determined by placing the peg lids with the biofilm formed onto microplates containing twofold diluted antibiotics. Biofilm prevention concentration (BPC) was determined after biofilm was formed directly into antibiotic contact. Optical density was measured after 6 and 24 hours of incubation.

Results: CIP, TOB, CAZ and IMP showed, respectively, the following geometric mean values: MIC 1.3, 3.6, 12.1 and 4.9 mg/L; BIC-6-h 2.7, 7.2, 149.3 and 21.8 mg/L; BIC-24-h, 17.3, 37.3, 512.0 and 128.0 mg/L; BPC-6-h, 2.4, 2.7, 42.4 and 5.9 mg/L; BPC-24-h, 10.3, 11.2, 339.5 and 29.6 mg/L. These values showed CIP and TOB similar inhibitory activity when P. aeruginosa growth was either sessile or planktonic at 6-h incubation (BIC/MIC and BPC/MIC ratios of 2x). Higher concentrations were required for all antibiotics to reach BIC and BPC after a 24-h incubation period, with BIC/MIC ratios of 13x, 10x, 42x and 26x for CIP, TOB, CAZ and IMP, respectively, and BPC/MIC ratios of 8x, 3x, 28x and 6x, respectively. In all cases, inhibitory effects required higher concentrations than prevention ones.

Conclusion: Early antibiotic challenged of P. aeruginosa in CF patients might benefit of prevention of biofilm formation, particularly with TOB and CIP. Antibiotic concentration required to prevent biofilm formation was lower than that to inhibit formed biofilm. The BIC and BPC parameters have been postulated in the attempt to correlate in vitro measurements with therapeutic outcomes in CF patients with early P. aeruginosa colonisation biofilm treatment.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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