Heterogeneous mechanisms of azole resistance in Candida albicans clinical isolates from an HIV-infected patient on continuous fluconazole therapy for oropharyngeal candidosis

Abstract

Molecular mechanisms of azole resistance in Candida albicans include alterations in the target enzyme and increased efflux of drug, but the impact of specific treatment regimens on resistance has not been established. A patient with advanced AIDS was enrolled in a longitudinal study to receive continuous oral fluconazole (FLU) 200 mg/day for the treatment of oropharyngeal candidosis (OPC). Oral cultures were obtained at time of enrollment, during episodes of OPC and quarterly for surveillance. The patient had five symptomatic relapses on continuous FLU during 43 months. All OPC episodes were successfully treated with increasing doses of FLU although increased FLU MICs were detected for C. albicans isolates with progression of time. DNA-typing techniques demonstrated that resistance developed in a persistent strain of C. albicans. Both FLU-resistant and isogenic isolates with reduced susceptibility were detected in the same clinical samples through multiple episodes. Analysis of molecular mechanisms of resistance revealed overexpression of MDR and CDR genes encoding efflux pumps (but not ERG11) in isolates with decreased FLU susceptibility. In addition, the presence of the G464S amino acid substitution in their lanosterol demethylase, affecting its affinity for FLU, was also detected. However, other isogenic, but FLU-susceptible isolates recovered from the same samples did not harbour the mutation, indicating microevolution of yeast populations within the oral cavity. In this patient, the continuous antifungal pressure exerted by FLU resulted in development of resistance of multifactorial nature. Despite their clonal origin, different subpopulations of C. albicans demonstrated distinct resistance mechanisms, including concomitant presence and absence of functional point mutations in ERG11 genes.

Overexpression and mutation as a genetic mechanism of fluconazole resistance in Candida albicans isolated from human immunodeficiency virus patients in Indonesia

“…S1, available in the online Supplementary Material). This shows that genetic polymorphisms of CYP51 are highly permissive to structural changes (Lee et al, 2004;Martínez et al, 2002).…”

Comparative Evaluation of Etest and Sensititre YeastOne Panels against the Clinical and Laboratory Standards Institute M27-A2 Reference Broth Microdilution Method for Testing Candida Susceptibility to Seven Antifungal Agents

“…Heteroresistance, or selection of a resistant subpopulation of cells from a population of predominantly susceptible cells, could account for such a phenomenon. Heteroresistance has been described in both Cryptococcus neoformans and C. albicans (15,16,29). The molecular mechanism associated with heteroresistance in C. albicans, i.e., the upregulation of CDR genes responsible for encoding cell wall pumps that infer cross-resistance among azoles, has also been associated with the development of fluconazole resistance in C. glabrata (3,27,28).…”

“…Accordingly, antifungal prophylaxis is routinely used in several populations considered at high risk for candidiasis, and breakthrough infections in patients on such prophylactic regimens are increasingly reported. The breakthrough organisms often have higher MICs of the drug to which they were exposed, and some may exhibit heteroresistance (14)(15)(16) and cross-resistance to one or more additional agents (1,11,33,34). Although fluconazole and, more recently, voriconazole, have been widely used as prophylactic agents, the introduction of newer agents and several supporting recent studies will likely increase the spectrum of agents used for this purpose.…”

The ABCs of Candida albicans Multidrug Transporter Cdr1

“…Upregulation of CDR genes was also observed in azole-resistant (AR) isolates from a marrow transplantation patient with disseminated candidiasis (17,18). Investigation of serial C. albicans isolates from HIV patients undergoing fluconazole therapy for repeated oropharyngeal candidiasis episodes also showed overexpression of the CDR1 and CDR2 genes (19,20). As discussed before, the members of both the ABC and MFS superfamilies contribute to MDR in C. albicans; however, only CDR1 and CDR2 of the 19 members of the ABC family and MDR1 of a fairly large number of MFS transporters have well-documented roles in clinical drug resistance (21,22).…”