Synergistic Antifungal Activity of Chitosan with Fluconazole against Candida albicans, Candida tropicalis, and Fluconazole-Resistant Strains

Abstract

(1) Background: Few antifungal drugs are currently available, and drug-resistant strains have rapidly emerged. Thus, the aim of this study is to evaluate the effectiveness of the antifungal activity from a combinational treatment of chitosan with a clinical antifungal drug on Candida albicans and Candida tropicalis. (2) Methods: Minimum inhibitory concentration (MIC) tests, checkerboard assays, and disc assays were employed to determine the inhibitory effect of chitosan with or without other antifungal drugs on C. albicans and C. tropicalis. (3) Results: Treatment with chitosan in combination with fluconazole showed a great synergistic fungicidal effect against C. albicans and C. tropicalis, but an indifferent effect on antifungal activity when challenged with chitosan-amphotericin B or chitosan-caspofungin simultaneously. Furthermore, the combination of chitosan and fluconazole was effective against drug-resistant strains. (4) Conclusions: These findings provide strong evidence that chitosan in combination with fluconazole is a promising therapy against two Candida species and its drug-resistant strains.

Antimicrobial Actions and Applications of Chitosan

“…The mechanisms of action of chitosan against bacteria and fungi have been investigated and reported in many articles [ 72 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 ]. Although the antimicrobial properties of chitosan are highly associated with its structure, physicochemical characteristics, and environmental conditions, in addition to the reactive hydroxyl groups at the C-3 and C-6 positions [ 4 , 37 , 39 , 43 , 90 , 103 , 105 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 ], the mode of action of chitosan against microbes can be classified as extracellular effects, intracellular effects, or both based on the targeting site of the antimicrobial effects [ 36 , 68 ,…”

“…Chitosan has been shown to have fungicidal effects on several fungal pathogens in plants and humans [ 82 , 83 , 108 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 ]. Its antifungal properties are mainly related to the interaction of chitosan with the cell wall or cell membrane.…”

“…For example, the opposite characteristics of chitosan-sensitive and chitosan-resistant Neurospora crassa strains are related to the content of unsaturated fatty acids on the cell membranes [ 150 ]. These data may account for, at least in part, why Candida albicans , Candida tropicalis , and other Candida species have remarkable differences in susceptibility to the same chitosan [ 83 , 152 ]. Indeed, C. tropicalis exhibited an increase in susceptibility of more than 1,000-fold to certain chitosans compared with C. albicans [ 83 , 152 ].…”

“…These data may account for, at least in part, why Candida albicans , Candida tropicalis , and other Candida species have remarkable differences in susceptibility to the same chitosan [ 83 , 152 ]. Indeed, C. tropicalis exhibited an increase in susceptibility of more than 1,000-fold to certain chitosans compared with C. albicans [ 83 , 152 ]. Similarly, in addition to its extracellular antifungal effects, low-MW chitosan is able to penetrate the cell wall and cell surface, leading to the inhibition of DNA/RNA and protein synthesis [ 39 , 68 , 82 , 91 , 122 , 125 , 132 ].…”

“…A major antimicrobial effect of chitosan is electrostatic interactions between this cationic molecule and negatively charged cell walls [ 72 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 ]. The pKa values of the amino groups of chitosan are 6.3–6.5, indicating that it is insoluble in alkaline solutions, organic solvents, and water when the pH is higher than 6.5 [ 36 , 68 , 90 , 103 , 107 , 121 ].…”