Candida tropicalis is a common species related to nosocomial candidemia and candiduria. Most Candida spp. infections are associated with biofilm formation on implanted medical devices or on host epithelial cell surfaces. Sessile cells display phenotypic traits dramatically different from those of their free-living, planktonic counterparts, such as increased resistance to antimicrobial agents and to host defenses. The characteristics of C. tropicalis biofilm formation in vitro are described. By an XTT-reduction assay, an increase in metabolic activity was observed up to 24 h of biofilm formation, and this activity showed a linear relationship with sessile cell density. Scanning electron microscopy was used to further characterize C. tropicalis biofilms. The initial adherence of yeast cells was followed by germination, microcolony formation, filamentation and maturation at 24-48 h. Mature biofilms consisted of a dense network of yeast cells and filamentous forms of C. tropicalis. Increased resistance of sessile cells against fluconazole and amphotericin B was also demonstrated. Real-time reverse transcription-PCR quantification showed that sessile cells overexpressed ERG11 (coding for lanosterol 14 alpha-demethylase) and MDR1 (coding for an efflux protein belonging to the major facilitator superfamily). These mechanisms may contribute to the fluconazole resistance of the C. tropicalis biofilm.

The aims of this study were to evaluate the epidemiology of nosocomial candidemia in a tertiary hospital in South Brazil and the in vitro antifungal susceptibility of isolates. Blood strains from 108 patients were identified by PCR-based method. Some 30.5 % of candidemia were caused by Candida tropicalis, 28.7 % were due to Candida albicans, 24.1 % with Candida parapsilosis sensu stricto, 8.3 % with Candida glabrata sensu lato, 1.8 % involved Candida krusei and 6.6 % with other species. Candidemia was more common in intensive care unit settings (66 %). In vitro susceptibility to antifungal drugs was determined by a microdilution method; and new species-specific clinical breakpoints for fluconazole and voriconazole were applied. Overall susceptibility rates were 100 % for itraconazole, 91 % for fluconazole, 98 % for voriconazole and 99 % for amphotericin B. Fluconazole resistance was mostly among C. parapsilosis sensu stricto isolates (26.9 %). Most of the findings reported here agreed with epidemiological features common to other tertiary hospitals in Brazil; but also revealed some peculiarities, such as a high frequency of C. tropicalis associated with candidemia. Besides, high rate of fluconazole resistance among C. parapsilosis stricto sensu isolates was obtained when applying the new species-specific clinical breakpoints.

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Non-albicans Candida species were more frequently isolated in the hospital. Fluconazole resistance was a rare finding in our study.

Although haemolytic factor is known to be a putative virulence factor contributing to pathogenicity in Candida species, its production by Candida tropicalis is poorly understood. In this study, we analysed the culture conditions under which C. tropicalis can display haemolytic factor on plate assay and the secretion of haemolytic factor in liquid medium by clinical isolates obtained from different specimens. All the tested isolates exhibited an internal translucent ring, resembling beta-haemolysis, surrounding by a peripheral greenish-grey halo on sheep blood agar medium. Similar haemolytic pattern was observed on human blood enriched medium. Furthermore, incubation either under normal atmosphere or under increased CO(2) had no effect on haemolysis. Overall, no differences were observed on beta-haemolytic activities (P > 0.05) among tested isolates of C. tropicalis. In glucose-limited medium (RPMI 1640 with 0.2% glucose), none of the isolates induced haemolysis on red blood cells. Similarly to found on plate assays, there were no significant differences (P > 0.05) in the activity of secreted haemolytic factor in liquid medium among C. tropicalis isolates. However, after growth, the number of yeast cells varied among isolates revealing different efficiencies of haemolytic factor production. Haemolytic activity was neither inhibited by heat treatment (100 °C) nor by the addition of pepstatin A. The obtained results extend our knowledge about haemolytic factor production by Candida species.

Although Candida tropicalis has become an increasingly important human pathogen, little is known regarding its potential to cause disease. In this study we evaluated the phenotypic switching ability of C. tropicalis and analyzed the effect of switching on biological properties related to virulence factors. We demonstrated that C. tropicalis switched spontaneously, reversibly and at high frequency (10(-1) to 10(-3)) when grown on yeast extract-peptone-D-glucose (YPD) agar medium. Phenotypic switching in five clinical isolates of C. tropicalis resulted in colonies exhibiting the following morphologies: crepe, rough, crater, irregular center, mycelial and diffuse. The majority of the variant colonies were associated with higher percentages of filamentous growth relative to their parental unswitched isolates. Significant differences (P < 0.05) in the production of hemolytic factor were found between most of the switched variants and their respective parental counterparts. Variant colonies exhibiting the crepe (derived from isolates 49.07 and 100.10) and rough phenotype (derived from isolate 49.07) had higher biofilm formation than their parental counterparts exhibiting a smooth dome surface (P < 0.05). Our data revealed that switching was correlated with changes in the in vitro minimum inhibitory concentrations (MICs) of a subset of the switched variants phenotypes to itraconazole. While the MIC to itraconazole was higher for crepe variant compared with its parental isolate 49.07, the rough variant of 100.10 had a lower MIC to this antifungal agent. The presented data support the role of phenotypic switching in promoting changes in phenotypic expression of putative virulence traits and itraconazole susceptibility of clinical isolates of C. tropicalis.

The aim of this study was to determine in vitro haemolytic and protease activities of Candida parapsilosis and Candida tropicalis isolates, obtained from anatomically distinct sites. Analysis of haemolytic activity of C. parapsilosis and C. tropicalis isolates obtained from the same anatomic site revealed that C. tropicalis isolates from blood had statistically higher activity (P < 0.05) than C. parapsilosis. On comparison of haemolytic activities of Candida isolates obtained from different anatomic sites, C. parapsilosis isolates from tracheal secretion were found to have higher activity than blood isolates. Protease activity was detected in the majority of the isolates analysed. Analysis of proteinase activity of C. parapsilosis and C. tropicalis isolates obtained from the same anatomic site revealed that C. parapsilosis isolates from tracheal secretion had statistically higher activity than C. tropicalis isolates. On comparison of proteinase activities of Candida isolates obtained from different anatomic sites, C. parapsilosis isolates from tracheal secretion were found to have higher activity than blood and superficial lesions isolates. Furthermore, C. tropicalis isolates from superficial lesions had higher activity than tracheal secretion isolates. Our results show the potential of C. parapsilosis and C. tropicalis isolates, obtained from distinct anatomic sites, to produce haemolytic factor and proteinases. Anatomic sites of isolation seem to be correlated with these activities, particularly for C. parapsilosis isolates.

INTRODUÇÃO: Leveduras do gênero Candida são responsáveis pela maioria das infecções fúngicas em humanos. Candida tropicalis tem sido uma das mais comumente isoladas dentre as espécies não-albicans. O objetivo foi analisar a hemólise in vitro promovida por isolados clínicos de C. tropicalis provenientes de sangue e outras amostras clínicas de pacientes internados no Hospital Universitário da UEL, PR-Brasil. MÉTODOS: Foi avaliada a hemólise promovida por 28 isolados clínicos de C. tropicalis, sendo os isolados agrupados em classes de acordo com os níveis de hemólise. RESULTADOS: A maioria dos isolados de sangue apresentou hemólise fraca (+), enquanto as classes de hemólise forte (+++) e muito forte (++++) foram as predominantes nos isolados de outras amostras clínicas como urina, lesão de unha e secreção traqueal, embora não tenham sido detectadas diferenças estatísticas (p>0,05). CONCLUSÕES: Isolados de C. tropicalis, obtidos de diferentes amostras clínicas, apresentam capacidade de promover hemólise in vitro.