Cellular characterisation of Candida tropicalis presenting fluconazole-related trailing growth.
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.
Laboratório de Bacteriologia/Micologia, Instituto de Biologia do Exército, Rio de Janeiro, Brasil.
Marcos
M
Dornelas-Ribeiro
Eliane Olmo
EO
Pinheiro
Carolina
C
Guerra
Lys Adriana
LA
Braga-Silva
Silvia Maia Faria de
SM
Carvalho
André Luis Souza dos
AL
Santos
Sonia
S
Rozental
Sergio Eduardo Longo
SE
Fracalanzza
D000935:Antifungal Agents / Q000494:pharmacology*; D041022:Candida tropicalis / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D015725:Fluconazole / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D046529:Microscopy, Electron, Transmission; D013997:Time Factors
D000935:Antifungal Agents; D015725:Fluconazole