Antibiofilm effects of amoxicillin–clavulanic acid and levofloxacin in patients with chronic rhinosinusitis with nasal polyposis

Microbial biofilms have been implicated in the pathogenesis of chronic rhinosinusitis with nasal polyposis (CRSwNP). The aim of our study was to evaluate in vitro effects of amoxicillin–clavulanic acid and levofloxacin on biofilm formation by bacterial species isolated from sinus tissue in patients with CRSwNP.

The sinus mucosal specimens were harvested from the upper parts and roof of ethmoid cavity of 48 patients with CRSwNP. Each sample was washed thoroughly in three separate beakers of sterile saline to remove any planktonic bacteria and further subjected to microbiology analysis. The biofilm-forming capacity of isolated strains was detected by microtiter-plate method and the effects of subinhibitory (1/2× to 1/16× MIC) and suprainhibitory concentrations (4, 8, 16, 32, and 64 µg/ml) of amoxicillin–clavulanic acid and levofloxacin on biofilm production were investigated.

Bacterial strains were isolated in 42 (87.5%) patients: one microorganism in 80.9% and two microorganisms in 19.1% of patients. The most prevalent bacteria in CRSwNP biofilms were Staphylococcus epidermidis (34%) and S. aureus (28%) followed by S. haemolyticus (12%), Pseudomonas aeruginosa (8%), Moraxella catarrhalis (6%), Streptococcus pneumoniae (6%), and other staphylococci (6%). Subinhibitory concentrations of amoxicillin–clavulanic acid and levofloxacin significantly reduced biofilm formation (p < 0.01 and p < 0.05, respectively), with better efficacy of amoxicillin–clavulanic acid (1/2–1/8× MIC) on staphylococci and levofloxacin (1/2– 1/4× MIC) on M. catarrhalis and P. aeruginosa biofilm formation. Suprainhibitory concentrations of both tested antibiotics (4–64 µg/ml) significantly eradicated mature biofilms of staphylococci (p < 0.01). The effect of levofloxacin on eradication of staphylococcal biofilms was more noticeable, compared to the effect of amoxicillin–clavulanic acid (p < 0.01). Suprainhibitory concentrations of both tested antibiotics had no effect on eradication of previously formed M. catarrhalis and P. aeruginosa biofilms (p > 0.05).

The amoxicillin–clavulanic acid and levofloxacin are shown to be potent antibiofilm agents in patients with CRSwNP. The effects of tested compounds depend on bacterial species and the volume of formed biofilm.