Use of an in vitro assay for determination of biofilm-forming capacity of bacteria in chronic rhinosinusitis

Background: Bacterial biofilms are increasingly implicated in the pathogenesis of chronic disease and have been established in several chronic ear, nose, and throat conditions, including chronic sinusitis (CRS). However, this relies on specialized imaging methods not widely available. We wished to assess the capacity of an easily performed, inexpensive in vitro test to assess biofilm production by bacteria recovered from individuals with CRS with or without nasal polyposis. Methods: Bacterial isolates were recovered from patients consulting an academic tertiary rhinology practice. Biofilm formation was determined with an in vitro staining method using crystal violet. Ten isolates of Pseudomonas aeruginosa, Staphylococcus aureus, and 11 of coagulase-negative staphylococcus from patients with CRS having previously undergone endoscopic sinus surgery for > 1 year were assessed. Samples were cultured 24 hours at 37 degrees C on 96-well plates in tryptic soy broth 0.5% glucose medium. After staining with crystal violet, optical density at 570 nm was measured to quantify biofilm production. Biofilm-forming capacity was compared with positive and negative controls for each species obtained from commercial sources. Results: Positive controls all grew biofilms, with a tendency of lesser biofilm formation at higher dilutions. Twenty-two of 31 clinical samples produced a biofilm greater or equal to the positive control. Biofilm was recovered consistently for all three species studied. Conclusion: This in vitro assessment method is capable of detecting biofilm-forming capacity in bacteria recovered from individuals with CRS. This simple assay may be a useful complement to existing techniques for clinical research.