Cellular characterisation of Candida tropicalis presenting fluconazole-related trailing growth

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.

Effect of a Silver Nanoparticles Solution onStaphylococcus aureusandCandidaspp.

“…Moreover, the amount of alkali-insoluble glucans, relative to both total wall mass and total glucan, is lower than those in C. albicans, suggesting that there are fewer cross-links between glucan and chitin in the cell wall of C. glabrata [31]. Although there is less information available on C. tropicalis, electron micrographs also have shown yeast cells presenting a compact, double cell wall (average thickness of 0.13 m) [32], with an outer layer with high electron density and an inner layer with less electron density [33]. Therefore, since the cell walls of pathogenic fungi form the first point of contact with the environment, these differences in architecture and components among Candida species probably may have contributed to the higher MIC and MFC values observed for planktonic C. glabrata cells compared to C. tropicalis and C. albicans cells.…”

Evaluation of antifungal effect of iron‐oxide nanoparticles against different Candida species

“…In addition, the amount of alkali‐insoluble glucans, relative to both total wall mass and total glucan, is less than those in C. tropicalis , indicating that there are less cross‐links between glucan and chitin in the cell wall of C. glabrata [40]. Moreover, C. tropicalis electron micrographs have shown that the yeast cells consists a compact, double cell wall (the average thickness of 0.13 μm), with an exterior layer with high electron density and an interior layer with less electron density [41]. Therefore, as regards that the cell walls of pathogenic fungi are the first point of contact with the surrounding environment, these differences in architecture and components between Candida spp.…”

Adaptation of the emerging pathogenic yeast Candida auris to high caspofungin concentrations correlates with cell wall changes

“…For a high number of isolates, echinocandins are unable to totally inhibit yeast growth. In particular, most isolates present paradoxical growth (PG, or Eagle effect) to CPF and exhibit "trailing" effect (TE, also known as residual growth or tolerance) to MICA and ANIDU in vitro during the antifungal susceptibility test (AFST) [30][31][32][33][34][35][36][37][38].…”