A Retrospective Analysis Of Biofilm Antibiotic Susceptibility Testing: A Better Predictor Of Clinical Response In Cystic Fibrosis Exacerbations

Background: Bacteria grow as biofilms within CF airways. However. antibiotic susceptibility testing is routinely performed on planktonically-growing bacteria. This study assessed whether CF patients infected with multiresistant organisms had improved clinical outcomes if given antibiotics that inhibited their biofilm-grown bacteria.Methods: 110 patients with pulmonary exacerbations were treated with intravenous antibiotics based on susceptibility testing of planktonically-growing bacteria. A retrospective analysis was done using bacterial isolates grown from their sputum at exacerbation. Each isolate was grown as a biofilm and combination antibiotic susceptibility testing was performed. Clinical outcomes in patients treated with biofilm-susceptible antibiotics were compared to those that were not.Results: 66 of 110 patients (60%) were treated with antibiotic combinations that inhibited all of their planktonically-grown bacterial isolates, however, when the same isolates were grown as biofilms, only 24 patients (22%) had all of their biofilm-growth isolates remaining susceptible to the antibiotics (P=<0.001). When patients with at least one biofilm-grown susceptible isolate (n=61) were compared to those with none (n=49), there was a significant decrease in sputum bacterial density (P=0.02) and length of stay (P=0.04) and a non-significant decrease in treatment failure. Survival analyses of time to next exacerbation showed non-significant trends favoring patients treated with biofilm-effective antibiotics.Conclusions: Most patients with CF exacerbations do not receive antibiotics that inhibit all biofilm-grown bacteria from their sputum at exacerbation. Patients treated with biofilm-effective therapy seemed to have improved clinical outcomes. (C) 2008 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.