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-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.
Keays
Tara
T
The Ottawa Health Research Institute, University of Ottawa, ON, Canada.
Ferris
Wendy
W
Vandemheen
Katherine L
KL
Chan
Francis
F
Yeung
Sau-Wai
SW
Mah
Thien-Fah
TF
Ramotar
Karam
K
Saginur
Raphael
R
Aaron
Shawn D
SD
D000328:Adult; D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D018441:Biofilms / Q000187:drug effects; D003550:Cystic Fibrosis / Q000150:complications* / Q000175:diagnosis / Q000188:drug therapy; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods*; D012141:Respiratory Tract Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology*; D012189:Retrospective Studies; D013183:Sputum / Q000382:microbiology; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents