Abstract
We assessed fluconazole susceptibility in 52 Candida tropicalis clinical strains using seven antifungal susceptibility methods, including broth microdilution (BMD) [standard M27 A3 (with neutral and acid pH), ATB Fungus 3, Vitek 2 system and flow cytometric analysis] and agar-based methods (disk diffusion and E-test). Trailing growth, detection of cell-associated secreted aspartic proteases (Saps) and morphological and ultrastructural traits of these clinical strains were also examined. The ranges of fluconazole 24 h-minimum inhibitory concentration (MIC) values were similar among all methods. The essential agreement among the methods used for MIC determinations was excellent and all methods categorised all strains as susceptible, except for one strain that showed a minor error. The presence of the trailing effect was assessed by six methods. Trailing positivity was observed for 86.5-100% of the strains. The exception was the BMD-Ac method where trailing growth was not observed. Morphological and ultrastructural alterations were detected in C. tropicalis trailing cells, including mitochondrial swelling and cell walls with irregular shapes. We tested the production of Saps in 13 C. tropicalis strains expressing trailing growth through flow cytometry. Our results showed that all of the C. tropicalis strains up-regulated surface Sap expression after 24 h or 48 h of exposure to fluconazole, which was not observed in untreated yeast strains. We concluded that C. tropicalis strains expressing trailing growth presented some particular features on both biological and ultrastructural levels.
Highlights
The increased incidence of systemic mycoses caused by Candida species in hospitalised patients is an important cause of morbidity and mortality worldwide, especially in critically ill patients (Warnock 2007, Mimica et al 2009, Ruan & Hsueh 2009)
Susceptibility tests - We tested the susceptibility to fluconazole and the phenotypic expression of trailing growth for 52 C. tropicalis strains using the standard broth microdilution (BMD)-N method and six other methods for comparison (Table I)
Data are shown as minimum inhibitory concentration (MIC) ranges and the MIC50% and MIC90%, except for the M44-A method, where the area of the inhibition zone around the disk was considered
Summary
The majority of the 52 C. tropicalis strains were isolated from clinical specimens collected from invasive infections, mainly blood (55%) and sterile fluids (24%), such as ascite and pleural effusions. Susceptibility tests - We tested the susceptibility to fluconazole and the phenotypic expression of trailing growth for 52 C. tropicalis strains using the standard BMD-N method and six other methods for comparison (Table I). The readings were discrepant at 48 h compared to those at 24 h, for the BMD-N and ATBF3 methods. The EA among all methods used for determining the MIC was excellent when compared with the BMD-N method, showing values of 98.1% for flow cytometry, 96.1% for Vitek 2 and ATBF3 and 92.3% for the BMD-Ac method. Thirteen discrepancies were noted between the MIC values of each strain for each method tested in relation to BMD-N, including 10 with the E-test, four with the BMD-Ac, two with the ATBF3 and two with the Vitek 2. Similar EA results for testing various methods against the standard method excluding the E-test have been reported in the literature (Pfaller et al 2007, Torres-Rodríguez & Alvarado-Ramírez 2007, Cuenca-Estrella et al 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
