Candida albicans Genes Modulating Echinocandin Susceptibility of Caspofungin-Adapted Mutants Are Constitutively Expressed in Clinical Isolates with Intermediate or Full Resistance to Echinocandins.

The opportunistic fungus Candida albicans is the leading cause of invasive candidiasis in immune-compromised individuals. Drugs from the echinocandin (ECN) class, including caspofungin, are used as a first line of therapy against invasive candidiasis. The only known mechanism of clinical resistance to ECNs is point mutations in the FKS1 gene, which encodes the drug target. However, many clinical isolates developed decreased ECN susceptibilities in the absence of resistance-associated FKS1 mutations. We have identified 15 C. albicans genes that contribute to decreased drug susceptibility. We explored the expression of these 15 genes in clinical isolates with different levels of ECN susceptibility. We found that these 15 genes are expressed in clinical isolates with or without FKS1 mutations, including those strains that are less susceptible to ECNs. In addition, FKS1 expression was increased in such less susceptible isolates compared to highly susceptible isolates. Similarities of gene expression patterns between isolates with decreased ECN susceptibilities in the absence of FKS1 mutations and clinically resistant isolates with mutations in FKS1 suggest that clinical isolates with decreased ECN susceptibilities may be a precursor to development of resistance.