Comportamento fenotípico e perfil de suscetibilidade de C. dubliniensis resistentes ao fluconazol frente a antifúngicos e associações

Abstract

Widespread and prolonged usage of azoles in recent years has led to the rapid development of drug resistance in Candida species. In Candida albicans, resistance to fluconazole causes cross-resistance to other antifungals and an increase in virulence, making treatment still more difficult because of the limited therapeutical options. Nonetheless, other species has emerged as significant pathogens of clinical importance. Fluconazole resistance has been clinically described in Candida dubliniensis isolates and it is easily induced by in vitro exposure to the drug, but little is known about its consequences. In the present study, two groups of C. dubliniensis isolates were evaluated and compared in some points with the closely related species, C. albicans. One group was composed by fluconazole-susceptible clinical isolates and the other was composed by fluconazole-resistant laboratory derivatives from the former, in order to examine the changes on phenotypic characteristics and antifungal susceptibility accompanying the development of resistance to fluconazole. Resistant derivatives showed minimal inhibitory concentrations equal or higher than 64 μg/mL and proved to keep most of phenotypic characteristics that were tested before resistance was induced. However, some strains were not found to produce pseudomycelia and chlamydospores. Against killer toxins, C. dubliniensis did not present biotypes enough to permit its differentiation from C. albicans. On the other hand, when proteinase activity was evaluated, C. albicans activity was significantly higher than C. dubliniensis . Resistant derivatives of C. dubliniensis showed proteinase activity similar to fluconazole-susceptible isolates, suggesting that fluconazole resistance may not necessarily result on an increase of virulence in this species. Partial atmosphere of CO2, fluconazole at subinhibitory concentrations, or combination of both conditions, as well as addition of antiretrovirals on induction culture medium did not influence on proteinase activity of C. albicans and C. dubliniensis isolates. Finally, fluconazole-resistant isolates showed cross-resistance with ketoconazole, itraconazole, ravuconazole and terbinafine. In addition, associations of amphotericin B or terbinafine with azoles resulted mainly on indifferent interactions. On fluconazole-susceptible isolates, the most positive interaction came from association of amphotericin B with voriconazole. When resistance was induced, the best activity was found when terbinafine was combined with itraconazole.