Chlorhexidine: beta-cyclodextrin inhibits yeast growth by extraction of ergosterol
I. R. Teixeira, K.V. Araújo, P.D. Sinisterra, R.E. Cortés, M.
Chlorhexidine (Cx) augmented with beta-cyclodextrin (-cd) inclusion compounds, termed Cx:-cd complexes, have been developed for use as antiseptic agents. The aim of this study was to examine the interactions of Cx:-cd complexes, prepared at different molecular ratios, with sterol and yeast membranes. The Minimal Inhibitory Concentration (MIC) against the yeast Candida albicans (C.a.) was determined for each complex; the MICs were found to range from 0.5 to 2 µg/mL. To confirm the MIC data, quantitative analysis of viable cells was performed using trypan blue staining. Mechanistic characterization of the interactions that the Cx:-cd complexes have with the yeast membrane and assessment of membrane morphology following exposure to Cx:-cd complexes were performed using Sterol Quantification Method analysis (SQM) and scanning electron microscopy (SEM). SQM revealed that sterol extraction increased with increasing -cd concentrations (1.71 × 10³; 1.4 × 10³; 3.45 × 10³, and 3.74 × 10³ CFU for 1:1, 1:2, 1:3, and 1:4, respectively), likely as a consequence of membrane ergosterol solubilization. SEM images demonstrated that cell membrane damage is a visible and significant mechanism that contributes to the antimicrobial effects of Cx:-cd complexes. Cell disorganization increased significantly as the proportion of -cyclodextrin present in the complex increased. Morphology of cells exposed to complexes with 1:3 and 1:4 molar ratios of Cx:-cd were observed to have large aggregates mixed with yeast remains, representing more membrane disruption than that observed in cells treated with Cx alone. In conclusion, nanoaggregates of Cx:-cd complexes block yeast growth via ergosterol extraction, permeabilizing the membrane by creating cluster-like structures within the cell membrane, possibly due to high amounts of hydrogen bonding.
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