Characterization of the Same Mutations in FCA1 Gene Associated With 5-FC Resistance of Candida albicans

Abstract

Background: Infections with 5-Fluorocytosine (5-FC)-resistant Candida albicans isolates in China have rarely been reported in clinical settings. Here, we present two 5-FC-resistant C. albicans (Ca5508 and CaBD4291) strains, separately isolated from two patients in China. Objectives:The main aim of this study was to characterize the key genetic mutations responsible for 5-FC resistance of the two drug-resistant isolates from the first affiliated hospital of Nanchang university. Methods: Multiplex PCR and phenotypic tests were used to confirm the isolates Ca5508 and CaBD4291. The standard micro broth dilution method M27-A3 was used for susceptibility testing of the two isolates. Molecular typing and analysis were performed by the combination of random amplified polymorphic DNA (RAPD), multilocus sequence typing (MLST), amplification and Sanger sequencing of 5-FC resistance-associated genes (FUR1 and FCA1). Results: The two isolates Ca5508 and CaBD4291 were identified as C. albicans by multiplex-PCR and phenotypic tests. The antifungal susceptibility testing showed that both of the isolates were resistant to 5-FC (MIC > 64µg/mL); Ca5508 was also resistant to fluconazole, ketoconazole, and itraconazole whereas CaBD4291 was not. The RAPD analysis demonstrated that the two isolates belonged to the same genotype. MLST typing identified two different sequence types: isolate CaBD4191 for ST732 and isolate Ca5508 for ST2975 (a new ST). Although the two STs were generally related, ST732 differed from ST2975 with 3/7 loci (AAC1, SYA1, VPS13). Surprisingly, the two isolates represented completely identical sequences of the two drug-associated genes FUR1 and FCA1. Compared to the susceptible reference strain SC5314, Ca5508 and CaBD4291 were found to have no mutation in FUR1; however, three missense mutations at positions 31, 83, and 107 of FCA1 were identified. Conclusions: Here, we newly reported two 5-FC-resistant clinical isolates of C. albicans that represented the same three mutations in FCA1 gene contributed to 5-FC resistance of C. albicans.