Comparison of Crystal Violet Staining Assay and XTT Methods in the Evaluation of Biofilm Formation in Candida parapsilosis Candidemia Isolates

Objective: Biofilm formation is one of the most important virulence factors of Candida species which leads to permanent infection foci by adhering to foreign materials and which are difficult to treat. Candida parapsilosis, which is one of the most common causes of candidemia in our country, is frequently isolated as a causative agent in catheterrelated infections. The most commonly used methods for evaluating the biofilm formation of Candida species are measuring cell viability with XTT (2,3-bis (2-methoxy-4-nitro-5sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide) and evaluating the total biofilm mass with crystal violet (CV). The aim of this study is to evaluate the biofilm formation ability of C. parapsilosis candidemia isolates by XTT and (CV) methods and compare these methods with each other. Materials and Methods: C. parapsilosis isolates sent from various hospitals between 2015 and 2019 were included in the study retrospectively, and the species-level identification was performed using the matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) The biofilm formation of the isolates was compared based on the optical density (OD) values obtained by crystal violet and XTT methods. The biofilm formation of the isolates was evaluated by categorizing them into low, medium and high biofilm groups as ± 20% according to the median value of all strains. Results: Totally, 79 C. parapsilosis candidemia isolates were included in this study and categorical compatibility between CV and XTT methods in low, medium and high biofilm groups was found as 69.6%, 60.6% and 73.9%, respectively. The OD values of the XTT method in the high biofilm group were found statistically significantly higher when compared with the values from the CV method. Conclusion: The compatibility of XTT and crystal violet methods in terms of biofilm measurement in C. parapsilosis isolates was considered acceptable, and no major variations were detected between the categories. According to these results, when evaluating the biofilm levels of C. parapsilosis isolates, high OD values obtained by the XTT method should be confirmed with the CV method.