Abstract
Drug-resistant Candida infection is a major health concern among immunocompromised patients. Antimicrobial photodynamic inactivation (PDI) was introduced as an alternative treatment for local infections. Although Candida (C.) has demonstrated susceptibility to PDI, high doses of photosensitizer (PS) and light energy are required, which may be harmful to eukaryotic human cells. This study explores the capacity of chitosan, a polycationic biopolymer, to increase the efficacy of PDI against C. albicans, as well as fluconazole-resistant clinical isolates in planktonic or biofilm states. Chitosan was shown to effectively augment the effect of PDI mediated by toluidine blue O (TBO) against C. albicans that were incubated with chitosan for 30 min following PDI. Chitosan at concentrations as low as 0.25% eradicated C. albicans; however, without PDI treatment, chitosan alone did not demonstrate significant antimicrobial activity within the 30 min of incubation. These results suggest that chitosan only augmented the fungicidal effect after the cells had been damaged by PDI. Increasing the dosage of chitosan or prolonging the incubation time allowed a reduction in the PDI condition required to completely eradicate C. albicans. These results clearly indicate that combining chitosan with PDI is a promising antimicrobial approach to treat infectious diseases.
Highlights
Chitosan is a natural linear polycationic biopolymer comprising N-acetyl-D-glucosamine and β-1,4-linked D-glucosamine
To examine the binding of toluidine blue O (TBO) to C. albicans and the survival fraction as it relates to incubation time, we measured the intensity of fluorescence after incubating 1 × 107 CFU/mL C. albicans with
Complete killing of C. albicans in the biofilm was observed after the incubation of chitosan for 2 h following photodynamic inactivation (PDI) with a TBO incubation time of 2 h (Figure 5B), suggesting that the augmentation of chitosan in PDI against biofilm cells is related to the level of damage
Summary
Chitosan is a natural linear polycationic biopolymer comprising N-acetyl-D-glucosamine and β-1,4-linked D-glucosamine. Candida species are approximately 25~50-times larger than bacterial test species and, contain a larger number of targets per cell [18] This may explain why C. albicans was shown to be susceptible to toluidine blue O (TBO) and methylene blue (MB) mediated PDI at higher doses of photosensitizers [19]. It has been demonstrated that PDI with MB or TBO, under conditions conducive to the effective killing of typical skin microbes, causes neither cytotoxicity [18,20,21] nor DNA damage to keratinocytes in vitro [22] Both humans and Candida are eukaryotic, and higher doses of photosensitizers or light irradiation might still be harmful to human cells. Following the administration of PDI, the addition of chitosan greatly augmented the killing of C. albicans and drug-resistant clinical isolates. Because the safety of chitosan as a biomaterial is well known, the combination of chitosan and PDI for the treatment of fungal infections shows considerable promise
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