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Background: This study assessed the potential effect of combining micafungin and tobramycin in vitro against biofilms of clinical Pseudomonas aeruginosa isolates.
Methods: Nine biofilm-positive clinical isolates of P. aeruginosa were used in this study. The minimum inhibitory concentrations (MICs) of micafungin and tobramycin for planktonic bacteria were determined using the agar dilution method. The planktonic bacterial growth curve was plotted for micafungin treatment. Biofilms of these nine strains were treated with different concentrations of micafungin and combined with tobramycin in microtiter plates. Biofilm biomass was detected by crystal violet staining and spectrophotometry. Phenotypic reduction in biofilm formation and the eradication of mature biofilm were significant based on average optical density (p < 0.05). The kinetics of micafungin combined with tobramycin to eradicate mature biofilms was investigated in vitro using the time-kill method.
Results: Micafungin exhibited no antibacterial effect on P. aeruginosa, and tobramycin minimum inhibitory concentrations (MICs) did not change in the presence of micafungin. Micafungin alone inhibited biofilm formation and eradicated established biofilms of all isolates in a dose-dependent manner, but the required minimum concentration varied. An increase in micafungin concentration resulted in an observed inhibition rate of 64.9% - 72.3% and achieved an eradication rate of 59.2% - 64.5%. Its combination with tobramycin exhibited synergistic effects, including inhibiting the biofilm formation of PA02, PA05, PA23, PA24, and PA52 isolates above 1/4 × MIC or 1/2 × MIC and eradicating mature biofilms of PA02, PA04, PA23, PA24, and PA52 above 32 × MIC, 2 × MIC, 16 × MIC, 32 × MIC, and 1 × MIC, respectively. Micafungin addition could eradicate biofilm-embedded bacterial cells more rapidly; at 32 mg/L, the biofilm eradication time lowered from 24 hours to 12 hours for the inoculum groups with 106 CFU/mL, and from 12 hours to 8 hours for 105 CFU/mL. Whereas at 128 mg/L, the time was lowered from 12 hours to 8 hours for the inoculum groups with 106 CFU/mL, and from 8 hours to 4 hours for 105 CFU/mL.
Conclusions: Micafungin showed good anti-biofilm activity at low concentrations. The combination of micafungin with tobramycin displayed a synergistic effect in controlling P. aeruginosa biofilm.
DOI: 10.7754/Clin.Lab.2022.220841
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