The burden of Candida parapsilosis bloodstream infections: from azole resistance to biofilm production

The aim of our work was to evaluate the incidence and antibiotype of Candida parapsilosis strains isolated from blood cultures at our hospital, the possible correlation between phenotypic and genotypic fluconazole resistance, and their ability to produce biofilm. Materials and Methods. C. parapsilosis strains were isolated from blood cultures by the BACTEC broth culture system and phenotypically identified by mass spectrometry (MALDI-TOF). Antifungal susceptibility testing (AST) was determined by broth micro- method (Sensititre YeastOne Colorimetric Broth). AST reading was performed using Clinical & Laboratory Standards Institute (CLSI) guidelines for the interpretation of Minimum Inhibitory Concentration (MIC) values. The different strains isolated were distinguished into three groups: Group 1 which comprised the strains susceptible to fluconazole (MIC ≤2 mcg/ml) and voriconazole (MIC ≤0.12 mcg/ml), Group 2A including the strains resistant to fluconazole (MIC ≥8 mcg/ml) and voriconazole (MIC ≥1 mcg/ml) and Group 2B into which isolates were resistant to fluconazole (MIC ≥8 mcg/ ml) and intermediate to voriconazole (MIC 0.25-0.5 mcg/ml). The study of genotypic resistance was conducted by Sanger sequencing of the ERG11 gene. Biofilm production was evaluated according to Ramage’s method, and a biofilm score (BS) was assigned as follows: low (1+,2+), medium (3+,4+) and good (5+,6+) producers. Results. ERG11 gene sequencing of 46 strains isolated in 2021 (46/100) mostly showed the presence of the Y132F and I197I (synonymous mutation) while the R398I and I261M mutations were quite rare with no apparent phenotypic resistance. Of these 46, 74% belonged to groups 2A and 2B, furthermore these strains showed low BS biofilm production (1+,2+). Regarding the biofilm analysis, a total of 71 C. parapsilosis strains were evaluated, of which 73.24 % (52/71) belonged to groups 2A and 2B and were associated with low BS (1+/2+) while 26.7 % (19/71) belonged to group 1 and expressed various levels of biofilm production (10/19 were medium and good BS producers). Discussion and Conclusions. The results obtained show that the strains harboring the Y132F mutation correlate with the phenotypic resistance to fluconazole whilst the I197I synonymous mutation does not impact the morphology of the target region and thus no associated resistance is observed. Additionally, it can be hypothesized that azoles, not being endowed with anti-biofilm activity, unlike echinocandins and liposomal amphotericin B, may have reduced efficacy in vivo, even against the phenotypically susceptible strains with medium and good BS scores. This can be especially true in cases of catheter-related candidemia.