A retrospective analysis of biofilm antibiotic susceptibility testing: A better predictor of clinical response in cystic fibrosis exacerbations

Abstract 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-grown 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.