Evaluation of the in vivo efficacy of topical tobramycin against Pseudomonas sinonasal biofilms

Background: There is increasing evidence that bacterial biofilms are present within the sinonasal mucosa of patients with medically recalcitrant chronic rhinosinusitis. The antibiotic concentrations needed to eradicate biofilms are much higher than those commonly used and pose an increased risk for systemic side effects. Topical medications are an alternative approach to deliver high concentrations to the mucosa while limiting systemic side effects. This is the first study to evaluate the effects of a topical antibiotic on Pseudomonas biofilms in an animal model of sinusitis. Methods: Pseudomonas sinusitis was established in nine rabbits. An irrigation catheter was placed within the lumen of the maxillary sinus, and the rabbits were irrigated with 7 days of normal saline or varying concentrations of tobramycin diluted in normal saline. Bacterial cfu were determined for nasal lavage fluid as well as physically disrupted mucosa, and scanning electron microscopy (SEM) of the mucosal surface was performed at the end of the study. Results: Increasing concentrations of topical tobramycin resulted in the eradication of viable bacteria within the lumen of the sinus but did not eradicate Pseudomonas attached to the mucosa. SEM detected biofilms within the mucosa even in those rabbits treated with high concentrations of topical tobramycin. Conclusions: Bacterial biofilms attached to the sinonasal mucosa are resistant to topical saline and tobramycin irrigation. SEM was useful in the identification of biofilms, but did not provide a quantitative evaluation for efficacy of treatment.