Candida parapsilosis Resistance to Fluconazole: Molecular Mechanisms and In Vivo Impact in Infected Galleria mellonella Larvae

Candida parapsilosis is the main non-albicans Candida species isolated from patients in Latin America. Mutations in theERG11 gene and overexpression of membrane transporter proteins have been linked to fluconazole resistance. The aim of this study was to evaluate the molecular mechanisms in fluconazole-resistant strains ofC. parapsilosis isolated from critically ill patients. The identities of the nine collectedC. parapsilosis isolates at the species level were confirmed through molecular identification with a TaqMan qPCR assay. The clonal origin of the strains was checked by microsatellite typing. TheGalleria mellonella infection model was used to confirmin vitro resistance. We assessed the presence ofERG11 mutations, as well as the expression ofERG11 and two additional genes that contribute to antifungal resistance (CDR1 andMDR1 ), by using real-time quantitative PCR. All of theC. parapsilosis (sensu stricto ) isolates tested exhibited fluconazole MICs between 8 and 16 μg/ml. Thein vitro data were confirmed by the failure of fluconazole in the treatment ofG. mellonella infected with fluconazole-resistant strains ofC. parapsilosis . Sequencing of theERG11 gene revealed a common mutation leading to a Y132F amino acid substitution in all of the isolates, a finding consistent with their clonal origin. After fluconazole exposure, overexpression was noted forERG11 ,CDR1 , andMDR1 in 9/9, 9/9, and 2/9 strains, respectively. We demonstrated that a combination of molecular mechanisms, including the presence of point mutations in theERG11 gene, overexpression ofERG11 , and genes encoding efflux pumps, are involved in fluconazole resistance inC. parapsilosis .