engleski

Antimicrobial potency of single and combined mupirocin and thymol against Staphylococcus aureus planktonic and biofilm growth

Staphylococcus aureus is one of the most commonly isolated microbes in chronic rhinosinusitis (CRS). The disease can be complicated due to the formation of a staphylococcal biofilm, which is more resistant to antimicrobials than planktonic bacteria. The purpose of this study was to investigate the antimicrobial efficacy of single mupirocin and monoterpene thymol as well as mupirocin-thymol combinations against S. aureus ATCC 29213 and 5 methicillin- resistant S. aureus strains (MRSA) grown in planktonic and biofilm form. Minimum inhibitory concentrations (MIC) against planktonic bacteria were determined using a two-fold microdilution method, according to CLSI guidelines. Biofilm was grown in Tryptic soy broth supplemented with 0.25% glucose in polystyrene tissue culture plates. Minimum biofilm eliminating concentrations (MBEC) and minimum biofilm inhibitory concentrations (MBIC) were determined by MTT reduction assay. Fractional Inhibitory Concentration Index (FICI) was applied to interpret the effects of mupirocin-thymol combinations. The MICs of mupirocin (0.125-0.156 μg/ml) were three orders of magnitude lower than the MICs of thymol (0.250-0.375 mg/ml). The FIC Index of mupirocin-thymol combinations showed a dominant indifferent effect. Mupirocin applied at a concentration range from 0.016 μg/mL to 2 mg/mL failed to destroy the biofilm. The MBECs of thymol were 2-fold higher than MICs. Mixtures of mupirocin and thymol exerted a potentiated biofilm eliminating effect. Both antimicrobials applied alone inhibited biofilm formation with MBICs close to their MICs. Dominant synergy in biofilm inhibitory efficacy was observed for mixtures of mupirocin and thymol. In conclusion, mupirocin in combination with the monoterpene thymol is more effective against staphylococcal biofilm than single compounds, suggesting their possible usage in CRS therapy in order to eliminate and prevent bacterial biofilm growth.

Biofilm; Staphylococci; mupirocin; thymol

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