Resistance Mechanisms in Clinical Isolates of Candida albicans

Abstract

Resistance to azole antifungals continues to be a significant problem in the common fungal pathogen Candida albicans. Many of the molecular mechanisms of resistance have been defined with matched sets of susceptible and resistant clinical isolates from the same strain. Mechanisms that have been identified include alterations in the gene encoding the target enzyme ERG11 or overexpression of efflux pump genes including CDR1, CDR2, and MDR1. In the present study, a collection of unmatched clinical isolates of C. albicans was analyzed for the known molecular mechanisms of resistance by standard methods. The collection was assembled so that approximately half of the isolates were resistant to azole drugs. Extensive cross-resistance was observed for fluconazole, clotrimazole, itraconazole, and ketoconazole. Northern blotting analyses indicated that overexpression of CDR1 and CDR2 correlates with resistance, suggesting that the two genes may be coregulated. MDR1 overexpression was observed infrequently in some resistant isolates. Overexpression of FLU1, an efflux pump gene related to MDR1, did not correlate with resistance, nor did overexpression of ERG11. Limited analysis of the ERG11 gene sequence identified several point mutations in resistant isolates; these mutations have been described previously. Two of the most common point mutations in ERG11 associated with resistance, D116E and E266D, were tested by restriction fragment length polymorphism analysis of the isolates from this collection. The results indicated that the two mutations occur frequently in different isolates of C. albicans and are not reliably associated with resistance. These analyses emphasize the diversity of mechanisms that result in a phenotype of azole resistance. They suggest that the resistance mechanisms identified in matched sets of susceptible and resistant isolates are not sufficient to explain resistance in a collection of unmatched clinical isolates and that additional mechanisms have yet to be discovered.

Genetic and phenotypic characterization of Candida albicans strains isolated from infectious disease patients in Shanghai

“…In our study, the combination of A114S and Y257H mutations was found in three itraconazole-resistant isolates and four itraconazole S-DD isolates, but none in susceptible isolates. G448E and G448R had been detected in fluconazole-and itraconazoleresistant isolates (Löffler et al, 1997;White et al, 2002). In our isolates, only one azole-resistant isolate (SH149) contained a G448E mutation, and no sensitive one did.…”

Transient Receptor Potential Channels in Sensory Neurons Are Targets of the Antimycotic Agent Clotrimazole

“…Finally, it cannot be excluded that the some neurons have mechanisms that mediate rapid extrusion or breakdown of CLT and thereby prevent it from significantly activating TRPV1/TRPA1. For example, it has been shown in yeast that high expression of drug extrusion pumps such as multidrug resistance 1 (MDR1) can lead to resistance to CLT (White et al, 2002;Looi et al, 2005). Independent of the mechanism, the lower cellular sensitivity to CLT compared with capsaicin or MO matches with the milder perceived sensory effects of CLT when applied to the tongue or mucous membranes.…”

Cyclic AMP Signaling Pathway Modulates Susceptibility of Candida Species and Saccharomyces cerevisiae to Antifungal Azoles and Other Sterol Biosynthesis Inhibitors

“…CDR1 encodes a multidrug transporter, and ERG11 encodes the azole target lanosterol demethylase. Both genes are commonly upregulated in azole-resistant clinical isolates (29,36); furthermore, in vitro treatment of susceptible FIG. 5.…”

“…Several mechanisms have been described for the azole resistance of C. albicans, including increased expression of ERG11 and of genes encoding multidrug transporters (encoded by CDR1, CDR2, and MDR1) (14,29,33,36). However, little is known about the regulatory pathways responsible for this increased expression.…”