A Dual Setback: Staphylococcus aureus Biofilms From Severe Chronic Rhinosinusitis Show Enhanced Virulence Capacity...

Staphylococcus aureus biofilms play a crucial role in chronic rhinosinusitis (CRS), leading to the persistence of symptoms. Severe CRS patients are frequently infected with S. aureus strains that exhibit higher biofilm properties (e.g., biomass, exoprotein production) compared to S. aureus from controls. S. aureus biofilms resist antibiotic treatment; however, the relationship between bacterial biofilm properties, antibiotic susceptibility, and CRS severity has not yet been defined and is the subject of this study.

S. aureus clinical isolates and reference strains, and matched clinical datasets were collected from CRS patients and controls (n  =  35). Antimicrobial susceptibility of the isolates to clindamycin, mupirocin, clarithromycin, doxycycline, and amoxicillin-clavulanic acid was determined by minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC).

S. aureus MBEC values (n  =  35) were significantly higher (up to 11 times) than the MIC for all five antibiotics (p < 0.001). Among the various antibiotics tested, mupirocin had the strongest antibiofilm activity and amoxicillin-clavulanic acid the weakest: at antibiotic concentrations that are deemed to indicate susceptibility or intermediate resistance when testing in planktonic form, 80% biofilm eradication was reached for all isolates using mupirocin and only 5/35 isolates using amoxicillin-clavulanic acid. The biofilm metabolic activity, biomass, colony-forming units, and exoprotein production were positively correlated with the MBEC values for amoxicillin-clavulanic acid and clarithromycin, but not for the other antibiotics. Lund-Mackay and Lund-Kennedy disease severity scores showed positive correlations with the MBEC values of clarithromycin.

These findings show that whilst severe CRS patients are frequently infected with S. aureus strains that exhibit higher biofilm-mediated virulence, these biofilms are also more difficult to control with standard of care antibiotics. Better personalized therapies are required to manage biofilm-mediated infections in severe CRS patients.