Effect of antimicrobial photodynamic therapy using toluidine blue on dual-species biofilms of Candida albicans and Candida krusei.

BACKGROUND: Although Candida albicans is the most frequent etiological agent of candidiasis, it has been reported a sizable number of infections related to the non-albicans Candida (NAC) species, Candida krusei. In addition, dual biofilms (biofilms composed by two species) may easily occur in vivo, becoming even more challenging the treatment of an infection. The fungicide effect of Photodynamic Therapy (PDT), using toluidine blue O (TBO) on both C. albicans and C. krusei development has been demonstrated. Thus, the objective of this study was to investigate the effects of PDT on dual-species biofilms of Candida albicans and Candida krusei. METHODS: The effect of PDT was observed on the metabolic activity of mature dual-species biofilms of Candida albicans and Candida krusei by a metabolic assay based on the reduction of XTT (2,3-bis(2­methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide sodium salt) assay and the identification of Candida albicans and Candida krusei was performed on CHROMagar Candida medium. RESULTS: it was observed a reduction of ∼30% in the metabolic activity of a mature biofilm treated with PDT, using 0.05 mg·mL-1 TBO and during biofilm formation a predominance of C. albicans on C. krusei was observed. The inhibition observed was related to reduction in the number of Colony Forming Units (CFU) of Candida albicans from 31.33 ± 3.7 to 17.0 ± 1.5. The number of CFU of C. krusei was not significantly modified. CONCLUSIONS: These results demonstrated the efficiency of PDT in inhibiting the dual-species biofilms of Candida albicans and Candida krusei by reducing C. albicans development.

The inhibitory effect of photodynamic therapy on dual-species biofilms of Candida albicans and Candida krusei can be determined by Candida albicans/Candida krusei ratio.

Candida krusei and Candida albicans present the ability to form communities of microorganisms called biofilms. Biofilms can be composed of a single species or more and are an important virulence factor. The inhibition of C. albicans and C. krusei as well as of their dual-species biofilms by antimicrobial Photodynamic Therapy (aPDT) has been demonstrated. This study aimed to investigate the effect of aPDT, with TBO, on dual-species biofilms of C. albicans and C. krusei using different culture mediums, RPMI-1640 and Sabouraud-dextrose broth (SDB) to produce biofilms presenting different C. albicans/C. krusei ratio. Biofilms formed using RPMI-1640 presented a higher C. albicans/C. krusei ratio, however, biofilms formed using SDB presented a predominance of C. krusei. The metabolic activity of biofilms produced using RPMI-1640 was inhibited by aP (∼40%), while biofilms produced using SDB were not affected by aPDT. In addition, biofilm biomass was reduced in biofilms produced using RPMI-1640 and treated with aPDT (∼20%). The results demonstrated that aPDT reduces C. albicans development in dual-species biofilms with C. krusei. However, no effect could be observed on C. krusei, demonstrating that C. krusei, when present in the structure of dual-species biofilms can be resistant to aPDT.