A Proteomic Landscape of Candida albicans in the Stepwise Evolution to Fluconazole Resistance

As an opportunistic fungal pathogen, Candida albicans is a major cause of superficial and systemic infections in immunocompromised patients. The increasing rate of azole resistance in C. albicans has brought further challenges to clinical therapy. In this study, we collected five isogenic C. albicans strains recovered over discrete intervals from an HIV-infected patient who suffered 2-year recurrent oropharyngeal candidiasis. Azole resistance was known from the clinical history to have developed gradually in this patient, and this was confirmed by MIC assays of each strain. Proteomic techniques can be used to investigate more comprehensively how resistance develops in pathogenic fungi over time. Our study is the first to use tandem mass tag (TMT) labeling combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) technology to investigate the acquired resistance mechanisms of serial C. albicans isolates at the proteomic level. A total of 4,029 proteins have been identified, of which 3,766 have been quantified. Compared with Ca1, bioinformatics analysis showed that differentially expressed proteins were mainly associated with aspects such as the downregulation of glycolysis/gluconeogenesis, pyruvate metabolism, fatty acid degradation, and oxidative stress response proteins in all four subsequent strains but, remarkably, the activation of amino acid metabolism in Ca8 and Ca14 and increased protection against osmotic stress or excessive copper toxicity, upregulation of respiratory chain activity, and suppression of iron transport in Ca17. By tracing proteomic alterations in this set of isogenic resistance isolates, we acquire mechanistic insight into the steps involved in the acquisition of azole resistance in C. albicans.