Carbon substrates promotes stress resistance and drug tolerance in clinical isolates of Candida tropicalis.

Candida tropicalis is a human pathogen and one of the most prevalent non-Candida albicans Candida (NCAC) species causing invasive infections. Azole antifungal resistance in C. tropicalis is also gradually increasing with the increasing incidence of infections. The pathogenic success of C. tropicalis depends on its effective response in the host microenvironment. To become a successful pathogen, cellular metabolism, and physiological status determine the ability of the pathogen to counter diverse stresses inside the host. However, to date, limited knowledge is available on the impact of carbon substrate metabolism on stress adaptation and azole resistance in C. tropicalis. In this study, we determined the impact of glucose, fructose, and sucrose as the sole carbon source on the fluconazole resistance and osmotic (NaCl), oxidative (H2O2) stress adaptation in C. tropicalis clinical isolates. We confirmed that the abundance of carbon substrates influences or increases drug resistance and osmotic and oxidative stress tolerance in C. tropicalis. Additionally, both azole-resistant and susceptible isolates showed similar stress adaptation phenotypes, confirming the equal efficiency of becoming successful pathogens irrespective of drug susceptibility profile. To the best of our knowledge, our study is the first on C. tropicalis to demonstrate the direct relation between carbon substrate metabolism and stress tolerance or drug resistance.

Isoespintanol Antifungal Activity Involves Mitochondrial Dysfunction, Inhibition of Biofilm Formation, and Damage to Cell Wall Integrity in Candida tropicalis.

The growing increase in infections caused by C. tropicalis, associated with its drug resistance and consequent high mortality, especially in immunosuppressed people, today generates a serious global public health problem. In the search for new potential drug candidates that can be used as treatments or adjuvants in the control of infections by these pathogenic yeasts, the objective of this research was to evaluate the action of isoespintanol (ISO) against the formation of fungal biofilms, the mitochondrial membrane potential (ΔΨm), and its effect on the integrity of the cell wall. We report the ability of ISO to inhibit the formation of biofilms by up to 89.35%, in all cases higher than the values expressed by amphotericin B (AFB). Flow cytometric experiments using rhodamine 123 (Rh123) showed the ability of ISO to cause mitochondrial dysfunction in these cells. Likewise, experiments using calcofluor white (CFW) and analyzed by flow cytometry showed the ability of ISO to affect the integrity of the cell wall by stimulating chitin synthesis; these changes in the integrity of the wall were also observed through transmission electron microscopy (TEM). These mechanisms are involved in the antifungal action of this monoterpene.

The Arylamidine T-2307 as a Novel Treatment for the Prevention and Eradication of Candida tropicalis Biofilms.

Candida tropicalis is an emerging pathogen with a high mortality rate due to its virulence factors, including biofilm formation, that has important repercussions on the public health system. The ability of C. tropicalis to form biofilms, which are potentially more resistant to antifungal drugs and the consequent increasing antimicrobial resistance, highlights an urgent need for the development of novel antifungal. The present study analyzed the antibiofilm capacity of the arylamidine T-2307 on two strains of Candida tropicalis. Antimicrobial activity and time-killing assays were performed to evaluate the anticandidal effects of T-2307, the antibiofilm ability on biomass inhibition and eradication was evaluated by the crystal violet (CV) method. Furthermore, in Galleria mellonella infected larvae an increased survival after pre-and post- treatment with T-2307 was observed. The MTT test was used to determine the viability of immortalized human prostate epithelial cells (PNT1A) after exposure to different concentrations of T-2307. Levels of interleukin IL-4, IL-8, IL-10 were quantified after Candida infection of PNT1A cells and treatment. Active doses of T-2307 did not affect the viability of PNT1A cells, and drug concentrations of 0.005 or 0.01 µg mL-1 inhibited the secretion of inflammatory cytokines. Taken together, these results provide new information on T-2307, indicating this drug as a new and promising alternative therapeutic option for the treatment of Candida infections.

Comparative proteomics and variations in extracellular matrix of Candida tropicalis biofilm in response to citral.

Candida tropicalis is an opportunistic human pathogen with an ability to cause superficial as well as systemic infections in immunocompromised patients. The formation of biofilm by C. tropicalis can cause dreadful and persistent infections which are difficult to treat due to acquired resistance. Presently, available anti-Candida drugs exhibit a high frequency of resistance, low specificity and toxicity at a higher dosage. In addition, the discovery of natural or synthetic anti-Candida drugs is slow paced and often does not pass clinical trials. Citral, a monoterpene aldehyde, has shown effective antimicrobial activities against various microorganisms. However, only few studies have elaborated the action of citral against the biofilm of C. tropicalis. In the present work, the aim was to study the fungicidal effect, differential expression of proteome and changes in extracellular matrix in response to the sub-lethal concentration (16 µg/mL) of citral. The administration of citral on C. tropicalis biofilm leads to a fungicidal effect. Furthermore, the differential expression of proteome has revealed twenty-five proteins in C. tropicalis biofilm, which were differentially expressed in the presence of citral. Among these, amino acid biosynthesis (Met6p, Gln1p, Pha2p); nucleotide biosynthesis (Xpt1p); carbohydrate metabolism (Eno1p, Fba1p, Gpm1p); sterol biosynthesis (Mvd1p/Erg19p, Hem13p); energy metabolism (Dnm1p, Coa1p, Ndk1p, Atp2p, Atp4p, Hts1p); oxidative stress (Hda2p, Gre22p, Tsa1p, Pst2p, Sod2p) and biofilm-specific (Adh1p, Ape1p, Gsp1p) proteins were identified. The overexpression of oxidative stress-related proteins indicates the response of biofilm cell to combating oxidative stress during citral treatment. Moreover, the upregulation of Adh1p is of particular interest because it subsidizes the biofilm inhibition through ethanol production as a cellular response. The augmented expression of Mvd1p/Erg19p signifies the effect of citral on ergosterol biosynthesis. The presence of citral has also shown an increment in hexosamine and ergosterol component in extracellular matrix of C. tropicalis biofilm. Hence, it is indicated that the cellular response towards citral acts through multifactorial processes. This study will further help in the interpretation of the effect of citral on C. tropicalis biofilm and development of novel antifungal agents against these potential protein targets.

Magnetically stimulated azo dye biodegradation by a newly isolated osmo-tolerant Candida tropicalis A1 and transcriptomic responses.

A recently isolated osmo-tolerant yeast Candida tropicalis A1, which could decolorize various azo dyes under high-salinity conditions, was systematically characterized in the present study. Stimulating dye-decolorization effectiveness and osmo-tolerance of the yeast by static magnetic field (SMF) was investigated and transcriptomic responses of the yeast to SMF was analyzed to propose possible mechanisms. The results demonstrated that the yeast A1 effectively decolorized (≥ 97.50% within 12 h) and detoxified (from high toxicity to low toxicity within 24 h) 70 mg/L Acid Red B (ARB) under the optimized conditions through a series of steps including naphthalene-amidine bond cleavage, reductive or oxidative deamination/desulfurization, open-loop of hydroxy-substituted naphthalene or benzene and TCA cycle. Moreover, dye decolorization performance and osmo-tolerance of the yeast A1 were further improved by 24.6 mT SMF. Genes encoding high-affinity hexose/glucose transporter proteins and NADH-ubiquinone oxidoreductase were up-regulated by 24.6 mT SMF, which might be responsible for the increase of dye decolorization. Significant up-regulation of glycerol-3-phosphate dehydrogenase and cell wall protein RHD3 suggested that osmo-tolerance was enhanced by 24.6 mT SMF through promoting production and intracellular accumulation of glycerol as compatible solute, as well as regulation of cell wall component. In conclusion, 24.6 mT SMF led to the up-regulation of related genes resulting in enhanced dye biodegradation efficiency and osmo-tolerance of the yeast A1.

Candida tropicalis RON1 is required for hyphal formation, biofilm development, and virulence but is dispensable for N-acetylglucosamine catabolism.

NDT80-like family genes are highly conserved across a large group of fungi, but the functions of each Ndt80 protein are diverse and have evolved differently among yeasts and pathogens. The unique NDT80 gene in budding yeast is required for sexual reproduction, whereas three NDT80-like genes, namely, NDT80, REP1, and RON1, found in Candida albicans exhibit distinct functions. Notably, it was suggested that REP1, rather than RON1, is required for N-acetylglucosamine (GlcNAc) catabolism. Although Candida tropicalis, a widely dispersed fungal pathogen in tropical and subtropical areas, is closely related to Candida albicans, its phenotypic, pathogenic and environmental adaptation characteristics are remarkably divergent. In this study, we focused on the Ron1 transcription factor in C. tropicalis. Protein alignment showed that C. tropicalis Ron1 (CtRon1) shares 39.7% identity with C. albicans Ron1 (CaRon1). Compared to the wild-type strain, the C. tropicalis ron1Δ strains exhibited normal growth in different carbon sources and had similar expression levels of several GlcNAc catabolic genes during GlcNAc treatment. In contrast, C. tropicalis REP1 is responsible for GlcNAc catabolism and is involved in GlcNAc catabolic gene expressions, similar to C. albicans Rep1. However, REP1 deletion strains in C. tropicalis promote hyphal development in GlcNAc with low glucose content. Interestingly, CtRON1, but not CaRON1, deletion mutants exhibited significantly impaired hyphal growth and biofilm formation. As expected, CtRON1 was required for full virulence. Together, the results of this study showed divergent functions of CtRon1 compared to CaRon1; CtRon1 plays a key role in yeast-hyphal dimorphism, biofilm formation and virulence. LAY ABSTRACT: In this study, we identified the role of RON1, an NDT80-like gene, in Candida tropicalis. Unlike the gene in Candida albicans, our studies showed that RON1 is a key regulator of hyphal formation, biofilm development and virulence but is dispensable for N-acetylglucosamine catabolism in C. tropicalis.

Adhesion of Candida tropicalis to polystyrene and epithelial cell lines: Insights of correlation of the extent of adherent yeast cells among distinct surfaces.

Candida tropicalis is an emerging fungal pathogen associated with high mortality. We aimed to compare adherence capability of C. tropicalis to polystyrene and epithelial cell lines (HeLa and Vero), and determine whether adherent blastoconidia is cell-type specific. Blastoconidia adhesion to epithelial cells and polystyrene were determined by crystal violet assay. The percentage of epithelial cells with adhered blastoconidia and the number of adhered blastoconidia per cell line were determined by light microscopy. The correlation between adhesion surfaces was assessed by Pearson's correlation coefficient. The adhesiveness of C. tropicalis to polystyrene was greater than that observed for ephitelial cells. High correlation values (r2 0.9999222, p 0.007941) were found for the adhesion capability between biotic and polystyrene surface for isolates 100.10 (obtained from blood) and 335.07 (obtained from tracheal secretion). The number of adherent blastoconidia per HeLa cell was greater in comparison to that observed for Vero cells (P<0.05). Further, high correlation (r2 1, p 0.0001) was found for the adhesion ability between HeLa cells and Vero cells. The results suggest a correlation of C. tropicalis adhesion capability among different surfaces, and that the adhesion to epithelial cells is specific to the cell type.

Vulvovaginal candidiasis in a murine model of diabetes emphasizing the invasive ability of etiological agents.

Aim: To compare the pathogenesis of vulvovaginal candidiasis by three Candida species in diabetic mice. Materials & methods: Estrogenized and diabetic mice were challenged with C. albicans, C. tropicalis and C. glabrata. Results: Diabetic animals infected with C. albicans and C. tropicalis maintained the highest fungal burden, despite of high levels of proinflammatory cytokines (IL-6 and TNF-α), respectively. For C. glabrata, the results were similar in diabetic and nondiabetic groups. Conclusion:C. tropicalis was as invasive as C. albicans, and both were more effective than C. glabrata. This ability was attributed to filamentation, which may be stimulated by glucose levels from vaginal fluid. In addition, the high burden may be attributed to the apparent immunological inefficiency of the diabetic host.

Targeting fungal virulence factor by small molecules: Structure-based discovery of novel secreted aspartic protease 2 (SAP2) inhibitors.

Secreted aspartic protease 2 (SAP2), a kind of virulence factor, is an emerging new antifungal target. Using docking-based virtual screening and structure-based inhibitor design, a series of novel SAP2 inhibitors were successfully identified. Among them, indolone derivative 24a showed potent SAP2 inhibitory activity (IC50 = 0.92 µM). It blocked fungi biofilm and hypha formation by down-regulating the expression of genes SAP2, ECE1, ALS3 and EFG1. As a virulence factor inhibitor, compound 24a was inactive in vitro and showed potent in vivo efficacy in a murine model of invasive candidiasis. It represents a promising lead compound for the discovery of novel antifungal agents.

NGT1 Is Essential for N-Acetylglucosamine-Mediated Filamentous Growth Inhibition and HXK1 Functions as a Positive Regulator of Filamentous Growth in Candida tropicalis.

Candida tropicalis is a pathogenic fungus that can cause opportunistic infections in humans. The ability of Candida species to transition between yeast and filamentous growth forms is essential to their ability to undergo environmental adaptation and to maintain virulence. In other fungal species, such as Candida albicans, N-acetylglucosamine (GlcNAc) can induce filamentous growth, whereas it suppresses such growth in C. tropicalis. In the present study, we found that knocking out the GlcNA-specific transporter gene NGT1 was sufficient to enhance C. tropicalis filamentous growth on Lee's plus GlcNAc medium. This suggests that GlcNAc uptake into C. tropicalis cells is essential to the disruption of mycelial growth. As such, we further studied how GlcNAc catabolism-related genes were able to influence C. tropicalis filamentation. We found that HXK1 overexpression drove filamentous growth on Lee's media containing glucose and GlcNAc, whereas the deletion of the same gene disrupted this filamentous growth. Interestingly, the deletion of the DAC1 or NAG1 genes impaired C. tropicalis growth on Lee's plus GlcNAc plates. Overall, these results indicate that HXK1 can serve as a positive regulator of filamentous growth, with excess GlcNAc-6-PO4 accumulation being toxic to C. tropicalis. These findings may highlight novel therapeutic targets worthy of future investigation.

Thymus vulgaris essential oil and thymol inhibit biofilms and interact synergistically with antifungal drugs against drug resistant strains of Candida albicans and Candida tropicalis.

Role of biofilm in disease development and enhance tolerance to antifungal drugs among Candida species has necessitated search for new anti-fungal treatment strategy. Interference in pathogenic biofilm development by new antifungal compounds is considered as an attractive anti-infective strategy. Therefore, the objective of this study was to evaluate Thymus vulgaris essential oil and its major active compound, thymol for their potential to inhibit and eradicate biofilms alone and in combination with antifungal drugs against Candida spp. with especial reference to Candida tropicalis. Anti-candidal efficacy of T. vulgaris and thymol in terms of minimum inhibitory concentration (MIC) was first determined to select the sub-MICs against C. albicans and C. tropicalis. Biofilm formation in the presence and absence of test agents was determined in 96-well microtiter plate by XTT reduction assay and effect of essential oils at sub-MICs of the test agents on biofilm development on glass surface was analysed by light and scanning electron microscopy. Synergistic interaction between essential oils and antifungal drugs were studied by checkerboard method. Effect of sub-MIC of T. vulgaris (0.5×MIC) and thymol (0.5×MIC) on biofilm formation showed a significant reduction (P<0.05) in biofilms. Light microscopy and SEM studies revealed disaggregation and deformed shape of C. albicans biofilm cells and reduced hyphae formation in C. tropicalis biofilm cells at sub-MICs of thymol. Significant effect of T. vulgaris and thymol was also recorded on pre-formed biofilms of both C. albicans and C. tropicalis. T. vulgaris and thymol also showed synergy with fluconazole against both in planktonic and biofilm mode of growth of C. albicans and C. tropicalis. However, synergy with amphotericin B is clearly evident only in planktonic Candida cells. Thyme oil and thymol alone or in combination with antifungal drugs can act as promising antibiofilm agent against drug resistant strains of Candida species and needs further in vivo study to synergise its therapeutic efficacy.

Antifungal and biofilm inhibitory effect of Cymbopogon citratus (lemongrass) essential oil on biofilm forming by Candida tropicalis isolates; an in vitro study.

ETHNOPHARMACOLOGICAL RELEVANCE: Cymbopogon citratus (lemongrass) essential oil has been widely used as a traditional medicine and is well known for antimicrobial properties. Therefore, it might be a potent anti-infective and biofilm inhibitive against Candida tropicalis infections. Until now, no ideal coating or cleaning method based on an essential oil has been described to prevent biofilm formation of Candida strains on silicone rubber maxillofacial prostheses, voice prostheses and medical devices susceptible to C. tropicalis infections. AIM OF THE STUDY: To investigate the antifungal and biofilm inhibitory effects of Cymbopogon citratus oil. Clinical isolates of C. tropicalis biofilms on different biomaterials were used to study the inhibitory effect. MATERIALS AND METHODS: The efficacy of Cymbopogon citratus, Cuminum cyminum, Citrus limon and Cinnamomum verum essential oils were compared on biofilm formation of three C. tropicalis isolates on 24 well polystyrene plates. C. citratus oil coated silicone rubber surfaces were prepared using hypromellose ointment as a vehicle. The antifungal tests to determine minimum inhibitory and minimum fungicidal concentrations were assessed by a microbroth dilution method and biofilm formation was determined by a crystal violet binding assay. RESULTS: C. tropicalis strains formed more biofilm on hydrophobic materials than on hydrophilic glass. C. citratus oil showed a high antifungal effect against all C. tropicalis strains. For comparison, C. limon oil and C. cyminum oil showed minor to no killing effect against the C. tropicalis strains. C. citratus oil had the lowest minimal inhibitory concentration of all essential oils tested and inhibited biofilm formation of all C. tropicalis strains. C. citratus oil coating on silicone rubber resulted in a 45-76% reduction in biofilm formation of all C. tropicalis strains. CONCLUSION: Cymbopogon citratus oil has good potential to be used as an antifungal and antibiofilm agent on silicone rubber prostheses and medical devices on which C. tropicalis biofilms pose a serious risk for skin infections and may cause a shorter lifespan of the prosthesis.

Phenotypic switching in Candida tropicalis alters host-pathogen interactions in a Galleria mellonella infection model.

Candida tropicalis is a human pathogen associated with high mortality rates. We have reported a switching system in C. tropicalis consisting of five morphotypes - the parental, switch variant (crepe and rough), and revertant (crepe and rough) strains, which exhibited altered virulence in a Galleria mellonella model. Here, we evaluate whether switching events may alter host-pathogen interactions by comparing the attributes of the innate responses to the various states. All switched strains induced higher melanization in G. mellonella larvae than that induced by the parental strain. The galiomicin expression was higher in the larvae infected with the crepe and rough morphotypes than that in the larvae infected with the parental strain. Hemocytes preferentially phagocytosed crepe variant cells over parental cells in vitro. In contrast, the rough variant cells were less phagocytosed than the parental strain. The hemocyte density was decreased in the larvae infected with the crepe variant compared to that in the larvae infected with the parental strain. Interestingly, larvae infected with the revertant of crepe restored the hemocyte density levels that to those observed for larvae infected with the parental strain. Most of the switched strains were more resistant to hemocyte candidacidal activity than the parental strain. These results indicate that the switch states exhibit similarities as well as important differences during infection in a G. mellonella model.

Poor prognosis of Candida tropicalis among non-albicans candidemia: a retrospective multicenter cohort study, Korea.

To evaluate clinical features and prognostic factors of non-albicans candidemia, we conducted a retrospective multicenter cohort study at 7 university hospitals in Korea from January 2010 to February 2016. A total of 721 patients with non-albicans candidemia were included in the analysis. C. tropicalis was most commonly identified (36.5%), followed by C. glabrata (27.2%), C. parapsilosis (25.7%), and C. krusei (2.4%). Clinical presentation of C. tropicalis candidemia was most severe with highest median C-reactive protein level (10.1 mg/dL) and Acute Physiology and Chronic Health Evaluation II score (14, both P ≪ 0.05). C. tropicalis showed the highest 14- and 30-day mortality (28.9% and 44.1%). In multivariate analysis, C. tropicalis infection was significantly related with 14- (P = 0.005) and 30-day mortality (P = 0.033). In conclusion, C. tropicalis infection presented most severely and showed worst clinical outcome among non-albicans candidemia.

Silver/silver chloride (Ag/AgCl) nanoparticles synthesized from Azadirachta indica lalex and its antibiofilm activity against fluconazole resistant Candida tropicalis.

In this study, latex of Azadirachta indica was used for the synthesis of silver nanoparticles (AgNP). UV-visible spectroscopy revealed the formation of AgNPs and the absorption band optimized at 442 nm. Fourier transform infrared (FTIR) spectroscopy shows different functional groups (carboxyl, amine and hydroxyl) of biomolecule which are responsible for reduction and capping process. X-ray diffraction (XRD) analysis confirms the nanoparticles are crystalline silver and cubic (AgCl) with face-centered cubic (Ag) types. Electron microscopics (SEM and TEM) were used to characterize the shape and size of the nanoparticles. The anticandidal and antibiofilm activity of AgNPs was using Fluconazole resistant clinical isolate of Candida tropicalis. The new approach of plant-mediated AgNPs synthesis appears to be cost-effective, eco-friendly and easy methods. The synthesized AgNPs considered as a novel and alternative agent to prevent C. tropicalis biofilms.

The general transcriptional repressor Tup1 governs filamentous development in Candida tropicalis.

Filamentous development is associated with the ability to cause infections and colonize the host in pathogenic Candida species. Candida tropicalis is one of the major fungal pathogens of humans. The conserved transcriptional repressor Tup1 plays a critical role in the regulation of transcription and filamentation in yeast species. Despite its central role, the full coding sequence of TUP1 has not been found in the reported genome sequence of C. tropicalis to date. In this study, we report the identification of Tup1 and characterize its role in filamentous growth in C. tropicalis. As expected, C. tropicalis Tup1 exhibits general conserved features to the orthologs of other fungi in terms of its structure and function. Deletion of TUP1 in C. tropicalis leads to increased filamentation under several culture conditions. However, Tup1 indeed exhibits species-specific roles in the regulation of filamentous development in C. tropicalis. For example, unlike the tup1/tup1 mutant of Candida albicans, the tup1/tup1 mutant of C. tropicalis is able to exist in the yeast form at low temperatures or in the presence of N-acetylglucosamine (GlcNAc). Acidic pH conditions also favor the yeast form of the tup1/tup1 mutant of C. tropicalis. Quantitative real-time PCR (qRT-PCR) assays indicate that Tup1 may regulate filamentous development through the transcriptional control of key filamentation regulators in C. tropicalis, such as Ume6, Brg1, Wor1, Sfl2, Ahr1, and Zcf3. Taken together, our findings demonstrate both conserved and species-specific roles of Tup1 in the regulation of filamentation and provide novel insights into the biology of C. tropicalis.

Electrospun essential oil-polycaprolactone nanofibers as antibiofilm surfaces against clinical Candida tropicalis isolates.

OBJECTIVE: As an approach to prevent biofilm infections caused by Candida tropicalis on various surfaces, determination of effect of biodegradable polycaprolactone nanofibers (PCLNFs) with different concentrations of two different essential oils were tested in this study. RESULTS: Both of the tested essential oils exhibited antifungal effect (minimal inhibitory concentration; 0.25-0.49 µL/mL, minimal fungicidal concentration; 0.25-0.49 µL/mL, depending on the C. tropicalis strain) (Zone of inhibition caused by 500 µL/mL concentration of oils; 28-56 mm). 0, 2, 4% clove oil PCLNFs and 0, 2, 4% red thyme oil-PCLNFs were free from bead formation and uniform in diameter. Diameters of all essential oil containing PCLNFs were ranged from 760 to 1100 nm and were significantly different from 0% essential oil-PCLNF (P < 0.05). 0, 2, 4% clove oil-PCLNFs were significantly more hydrophobic compared to 8% clove oil-PCLNF (P < 0.01), whereas 0% and 2% red thyme oil-PCLNFs were significantly more hydrophobic compared to 4% and 8% red thyme oil PCLNFs (P < 0.01). Highest amount of biofilm inhibition was observed by 4% clove oil-PCLNF and by 4% red thyme oil-PCLNF. CONCLUSIONS: Clove and red thyme oils may be used not only as antifungals but also as biofilm inhibitive agents on surfaces of biomaterials that are frequently contaminated by C. tropicalis, when they are incorporated into PCLNFs.

Candida tropicalis biofilm formation and expression levels of the CTRG ALS-like genes in sessile cells.

Candida tropicalis is an emergent pathogen with a high rate of mortality associated with it; however, less is known about its pathogenic capacity. Biofilm formation (BF) has important clinical repercussions, and it begins with adherence to a substrate. The adherence capacity depends principally on the cell surface hydrophobicity (CSH) and, at a later stage, on specific adherence due to adhesins. The ALS family in C. tropicalis, implicated in adhesion and BF, is represented in several CTRG genes. In this study, we determined the biofilm-forming ability, the primary adherence, and the CSH of C. tropicalis, including six isolates from blood and seven from urine cultures. We also compared the expression of four CTRG ALS-like genes (CTRG_01028, CTRG_02293, CTRG_03786, and CTRG_03797) in sessile versus planktonic cells, selected for their possible contribution to BF. All the C. tropicalis strains were biofilm producers, related to its filamentation capacity; all the strains displayed a high adherence ability correlated to the CSH, and all the strains expressed the CTRG genes in both types of growth. Urine isolates present, although not significantly, higher CSH, adherence, and biofilm formation than blood isolates. This study reveals that three CTRG ALS-like genes-except CTRG_03797-were more upregulated in biofilm cells, although with a considerable variation in expression across the strains studied and between the CTRG genes. C. tropicalis present a high biofilm capacity, and the overexpression of several CTRG ALS-like genes in the sessile cells suggests a role by the course of the biofilm formation.

In vitro interaction of Candida tropicalis biofilm formed on catheter with human cells.

Candida tropicalis has emerged as one of the major Candida non-C. albicans species, in terms of epidemiology and virulence. Despite its virulence, C. tropicalis pathogenic mechanism has yet not been fully defined. The current study aimed to demonstrate the interaction of mature C. tropicalis ATCC 750 biofilm formed on catheter with different human cell lines. In vitro mature (72 h) C. tropicalis biofilms were produced on small catheter fragments (SCF) and were mainly composed by blastoconidia. Then, migration of yeast cells from mature biofilm to human cell surfaces (HeLa and HUVEC) was investigated. After contact with both cell lines, the surface of SCF, containing mature C. tropicalis biofilm, exhibited predominantly the filamentous form. Meanwhile, fresh biofilm formed on human cell surfaces also revealed mainly of blastoconidia involved by extracellular matrix. Total biomass and metabolic activity from the remaining biofilm on SCF surface, after direct contact with human cells, exhibited a significant reduction. Mature C. tropicalis biofilm modified its extracellular matrix components, after contact with human cells. Thus, we described for the first time an easy and simple in vitro model with catheter, which could be a powerful tool for future studies that desires to elucidate the mechanisms involved in C. tropicalis biofilm.