Low pH nasal rinse solution enhances mupirocin antimicrobial efficacy

Abstract

Background: Chronic rhinosinusitis (CRS) is a common condition negatively impacting a patient’s quality of life. It has been hypothesized that bacterial biofilms are involved in the pathogenesis of CRS due to their persistence and difficulty to eradicate with conventional antibiotic therapy. Hence, the topical delivery of antibiotics via nasal rinse solution has gained a lot of attention due to the ability to deliver higher local concentrations, with less systemic absorption and side effects. This study investigates the efficacy of mupirocin dissolved in the 3 most commonly used sinus rinses in Australia Neilmed (isotonic saline), Flo Sinus Care (sodium chloride, sodium bicarbonate, potassium chloride, glucose anhydrous and calcium lactate and Pentahydrate) and FloCRS (sodium chloride, potassium chloride and xylitol). Methods: Planktonic and biofilm cultures of S. aureus (ATCC25923, 2 methicillin-resistant S. aureus (MRSA) (C222 and C263), and 2 methicillin-susceptible S. aureus (MSSS) (C311 and C349) clinical isolates) were treated with mupirocin dissolved in three sinus rinses (Neilmed, Flo Sinus Care and FloCRS with different pH). To establish whether pH was a significant factor in determining antibiotic activity, experiments with Flo CRS were performed both at pH 5.64 and elevated pH 7.7. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined for planktonic cells. The biofilm biomass and metabolic activity were assessed by using crystal violet assay and alamarBlue assay respectively. Results: The combination of mupirocin in low pH (pH 5.64) sinus rinse (FloCRS) had the highest efficacy in reducing the growth of S. aureus in both the planktonic and biofilm forms. Mupirocin diluted in FloCRS (pH 5.64) showed a significantly higher reduction in both biomass and metabolic activity than that was observed when mupirocin was diluted in Neilmed, Flo Sinus Care or FloCRS (pH 7.7). Conclusion: The choice of irrigant solution for topical mupirocin delivery appears to be important for antimicrobial activity. The delivery of mupirocin via low pH FloCRS could be useful in eliminating S. aureus biofilms present on the sinus mucosa of patients with CRS.