Effectiveness of topical antibiotics on Staphylococcus aureus biofilm
in vitro.Desrosiers M, Bendouah Z, Barbeau J.
Department of Otolaryngology-Head and Neck Surgery, University of
Montreal, Montreal, Canada. desrosiers_martin@hotmail.com

BACKGROUND: In vitro biofilm-producing capacity in isolates of
Staphylococcus aureus and Pseudomonas aeruginosa collected from the
sinus cavities after endoscopic sinus surgery (ESS) are associated
with a poor outcome in patients with chronic rhinosinusitis (CRS).
However, conventional oral antibiotic therapy is frequently
ineffective in eradicating bacteria in the biofilm form. Increasing
the concentration of antibiotics may offer a means of countering this
resistance. The aim of this study was to determine the in vitro
activity of moxifloxacin (MOXI) against S. aureus in biofilm form
(recovered from patients with CRS at least 1 year post-ESS). METHOD:
This study was performed in a research microbiology laboratory, where
five isolates of S. aureus with known biofilm-forming capacity were
cultured in Tryptic Soy Broth 0.5% glucose in 96-well plates at 37
degrees C for 24 hours. After visual confirmation of biofilm
formation, plates were incubated in phosphate-buffered saline (PBS) or
with MOXI at concentrations of 0.1x, Ix, 100x, and 1000x minimal
inhibitory concentration (MIC) for an additional 24 hours. Biofilm
from 3 wells of each concentration were collected and sonicated and
the number of viable bacteria was determined by serial dilution and
plating. RESULTS: After incubation, the number of viable bacteria was
similar for nontreated and MOXI-treated biofilms at MIC and sub-MIC
levels. However, MOXI at 1000x (0.1-0.2 mg/mL) gave a 2 to 2.5 log
reduction in number of viable bacteria. CONCLUSION: In vitro results
show that increased concentrations of antibiotics, easily attainable
in topical solutions, are effective in killing bacteria in bacterial
biofilms. This suggests a role for topical antibiotic therapies in the
treatment of biofilm infections.

PMID: 17424869 [PubMed - indexed for MEDLINE]

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