Antifungal susceptibility of Candida species to copper oxide nanoparticles on polycaprolactone fibers (PCL-CuONPs)

The integration of metallic or ceramic nanoparticles in polymer matrices has improved the antimicrobial and antifungal behavior, resulting in the search for composites with increased bactericidal and antimycotic properties. A polycaprolactone fibers with copper oxide nanoparticles was prepared. Polycaprolactone-copper fibers (PCL- CuONPs) were prepared into two major steps in situ method: (a) Synthesis of CuO particles, then (b) incorporation of polycaprolactone to electrospun process. The first step is the reduction of Cu+2 ions by gallic acid in N,N-dimethylformamide and tetrahydrofuran solution with the simple addition of polycaprolactone in the solution for the second electrospun step. Raman spectra provide information about the nature of the copper oxide synthesized. There are three Raman peaks in the sample, at 294 and 581 cm-1 and a very broad band from 400 to 600 cm-1 which are characteristics bands for CuO. Scanning electron microscopy (TEM) revealed copper oxide nanoparticles with semispherical shapes with diameter 35 ±11 nm. Dynamic light scattering (DLS) analysis showed uniform CuONPs in a range of 88±11 nm. Scanning electron microscopy (SEM) of PCL-CuONps reveled fibers with diameters ranging from 925 to 1080 nm were successfully obtained by electrospinning technique. Orientation, morphology and diameter were influenced by the increment on CuONPs concentration, with the smaller diameter present in samples prepared from low concentrated solutions. The antimycotic applicability of the composite was evaluated to determine the antifungal activity in three species of the genus Candida (Candida albicans, Candida glabrata and Candida tropicalis). PCL-CuONPs exhibit a considerable antifungal effect on all species tested. The preparation of PCL-CuONPs was simple, fast and low-cost for practical application as an antifungal dressing.

Anticandidal and In vitro Anti-Proliferative Activity of Sonochemically synthesized Indium Tin Oxide Nanoparticles

The present work demonstrates the synthesis, characterization and biological activities of different concentrations of tin doped indium oxide nanoparticles (Sn doped In2O3 NPs), i.e., (Sn/In = 5%, 10% and 15%). We have synthesized different size (38.11 nm, 18.46 nm and 10.21 nm) of Sn doped In2O3 NPs. by using an ultra-sonication process. The Sn doped In2O3 NPs were characterized by by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) which confirmed the successful doping of tin (Sn) with Indium oxide (In2O3). Anticandidal activity was performed by standard agar dilution method using Candida albicans for the study. The minimum inhibitory/fungicidal concentration (MIC/MFC) values recorded were, 8 & >8 mg/ml for pure In2O3 NPs, 4 & 8 mg/ml for 5%, 2 & 8 mg/ml for 10%, whereas 1 & >4 mg/ml for 15% Sn doped In2O3 NPs, respectively. The topographical alteration caused by Sn doped In2O3 NPs on Candida cells, was clearly observed by SEM examination. A significant enhancement in anticandidal activity was seen, when Candida cells were exposed to (Sn/In = 5%, 10% and 15%). Moreover, we have also evaluated the impact of Sn-In2O3 NPs on human colorectal carcinoma cells (HCT-116). The results demonstrated that Sn-In2O3 NPs (Sn/In = 5%, 10% and 15%), caused dose dependent decrease in the cancer cell viability as the low dosage (2.0 mg/mL) showed 62.11% cell viability, while 4.0, 8.0, 16.0, 32.0 mg/mL dosages showed 20.45%, 18.25%, 16.58%, and 15.58% cell viability. In addition, the treatment of Sn-In2O3 NPs also showed significant cellular and anatomical changes in cancer cells as examined by microscopes. We have also examined the impact of Sn-In2O3 NPs (5%, 10%, 15%) on normal cells (HEK-293) and the results demonstrate that Sn-In2O3 NPs did not reduce the cell viability of normal cells.

Design of Heptad Repeat Amphiphiles Based on Database Filtering and Structure-Function Relationships to Combat Drug-Resistant Fungi and Biofilms

Due to the emergence of reports of multidrug-resistant fungi, infections caused by multidrug-resistant fungi and biofilms are considered to be a global threat to human health due to the lack of effective broad-spectrum drugs. Here, we developed a series heptad repeat sequences based on an antimicrobial peptide database (APD) and structure-function relationships. Among the developed peptides, the target peptide ACR3 exhibited good activity against all fungi and bacteria tested, including fluconazole-resistant Candida albicans (C. albicans) and methicillin-resistant Staphylococcu saureus (S. aureus), while demonstrating relatively low toxicity and good salt tolerance. The peptide ACR3 inhibits the formation of C. albicans biofilms and has a therapeutic effect on mature biofilms in vitro and in vivo. Moreover, we did not observe any resistance of C. albicans and E. coli against the peptide ACR3. A series of assays and microscopy were used to analyze the antimicrobial mechanism. These results showed that the antimicrobial activity of the peptide ACR3 utilizes a multimodal mechanism that degrades the cell wall barrier, alters the cytoplasmic membrane electrical potential, and induces intracellular reactive oxygen species (ROS) production. In general, the peptide ACR3 is a potent antibacterial agent that shows great potential for use in biomedical coatings and healthcare formulas to combat the growing threat of fungal and bacterial infection.

In vitro synergism of a water insoluble fraction of Uncaria tomentosa combined with fluconazole and terbinafine against resistant non-Candida albicans isolates

CONTEXT

Uncaria tomentosa D.C. (Rubiaceae) has several biological activities, including activity against resistant Candida strains. The synergistic interaction with terbinafine or fluconazole can be an important alternative to overcome this resistance.

OBJECTIVES

The potential synergy between a water insoluble fraction (WIF) from Uncaria tomentosa bark and the antifungals terbinafine (TRB) and fluconazole (FLZ) against non-Candida albicans resistant strains was investigated.

MATERIALS AND METHODS

TRB and FLZ, alone and combined with WIF, were tested by the checkerboard procedure using the micro-dilution technique against seven isolates of Candida glabrata and C. krusei. The molecular interactions occurring outside the cell wall were evaluated by scanning electron microscopy, Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) analysis.

RESULTS

The checkerboard inhibitory assay demonstrated synergy for WIF:TRB and WIF:FLZ combinations, respectively. The best synergistic cell damage was demonstrated unequivocally for the associations of WIF and TRB (1.95:4.0 μg/mL) and WIF and FLZ (1.95:8.0 μg/mL). The comparison of the FT-IR spectra of the antifungal alone, and in combination with WIF, allows recognizing clear differences in 3000, 1600, 1400, and 700-800 cm^-1 bands. Additionally, modifications on TRB and FLZ thermograms were clearly noticed after their combination with WIF.

CONCLUSIONS

DSC and infrared analysis demonstrated intermolecular interactions between WIF and either TRB or FLZ. Hence, quite likely the synergistic effect is related to interaction events occurring outside the cell wall between antifungal and cat's claw proanthocyanidins. A direct action on the cell wall is suggested, without connection with the ABC efflux pump mechanism.

Convenient method for better preservation of fine structures of cultured macrophages and engulfed yeast cells by freeze-substitution fixation

Rapid freeze-freeze substitution after glutaraldehyde fixation (CF-FS method) obtained the natural and fine structures of macrophages and engulfed yeast cells. Culturing macrophages on single hole molybdenum grids placed in culture dishes made possible the rapid freezing of cells by the 'open sandwich method'. This method may be convenient when rapid-freezing cannot be performed immediately, or when a rapid-freezing device is not available in the lab.

Candida albicans and Candida dubliniensis: comparison of biofilm formation in terms of biomass and activity

Candida albicans and C. dubliniensis are two species responsible for oral candidiasis, especially in immunocompromised patients. Microbial infection is preceded by adherence and biofilm formation. Biofilm formation represents the most common form of C. albicans in the oral cavity and is considered to be one of the most important virulence factors. In this study, the biofilm formation ability of C. dubliniensis was compared with that of C. albicans in terms of biomass (quantified using crystal violet) and activity (assessed by formazan salts formation). Both species formed heterogeneous biofilms; however, species and strain variations were seen in the quantification of biomass and activity. There was no correlation between pseudohyphae formation and biofilm formation capability.

Effects of Selenium on Morphological Changes in Candida utilis ATCC 9950 Yeast Cells

This paper presents the results of microscopic examinations of the yeast cells cultured in yeast extract-peptone-dextrose (YPD) media supplemented with sodium selenite(IV). The analysis of the morphological changes in yeast cells aimed to determine whether the selected selenium doses and culturing time may affect this element accumulation in yeast cell structures in a form of inorganic or organic compounds, as a result of detoxification processes. The range of characteristic morphological changes in yeasts cultivated in experimental media with sodium selenite(IV) was observed, including cell shrinkage and cytoplasm thickening of the changes within vacuole structure. The processes of vacuole disintegration were observed in aging yeast cells in culturing medium, which may indicate the presence of so-called ghost cells lacking intracellular organelles The changes occurring in the morphology of yeasts cultured in media supplemented with sodium selenite were typical for stationary phase of yeast growth. From detailed microscopic observations, larger surface area of the cell (6.03 μm(2)) and yeast vacuole (2.17 μm(2)) were noticed after 24-h culturing in the medium with selenium of 20 mg Se(4+)/L. The coefficient of shape of the yeast cells cultured in media enriched with sodium selenite as well as in the control YPD medium ranged from 1.02 to 1.22. Elongation of cultivation time (up to 48 and 72 h) in the media supplemented with sodium selenite caused a reduction in the surface area of the yeast cell and vacuole due to detoxification processes.

Candida parapsilosis biofilm identification by Raman spectroscopy

Colonies of Candida parapsilosis on culture plates were probed directly in situ using Raman spectroscopy for rapid identification of specific strains separated by a given time intervals (up to months apart). To classify the Raman spectra, data analysis was performed using the approach of principal component analysis (PCA). The analysis of the data sets generated during the scans of individual colonies reveals that despite the inhomogeneity of the biological samples unambiguous associations to individual strains (two biofilm-positive and two biofilm-negative) could be made.

[Export of an invertase by yeast cells (Candida utilis)]

Export and accumulation of various forms of invertase (EC 3.2.1.26) in the cell wall and culture liquid of the yeast Candida utilis was investigated. It was found that the high-molecular-weight CW-form of invertase is present in the cell wall. This form is not exported into the culture liquid, and it is by a third more glycosylated than the previously described exported S-form. It was shown that one of the two liquid forms of invertase exported into the culture-the glycosylated S-form--is retained in the cell wall, while the other one--the nonglycosylated F-form--was not detected in the cell wall. Based on these results, as well as data on the distribution dynamics of the enzyme in the culture liquid and in the cell wall during different growth stages of a yeast culture, we suggested that the nonglycosylated form was exported into the culture liquid via the zone of abnormal cell wall permeability and the glycosylated forms of this enzyme (both exported and nonexported) did not use this pathway (the degree of N-glycosylation is an important factor determining the final localization of the enzyme).

Purpurin triggers caspase-independent apoptosis in Candida dubliniensis biofilms

Candida dubliniensis is an important human fungal pathogen that causes oral infections in patients with AIDS and diabetes mellitus. However, C. Dubliniensis has been frequently reported in bloodstream infections in clinical settings. Like its phylogenetically related virulent species C. albicans, C. Dubliniensis is able to grow and switch between yeast form and filamentous form (hyphae) and develops biofilms on both abiotic and biotic surfaces. Biofilms are recalcitrant to antifungal therapies and C. Dubliniensis readily turns drug resistant upon repeated exposure. More than 80% of infections are associated with biofilms. Suppression of fungal biofilms may therefore represent a viable antifungal strategy with clinical relevance. Here, we report that C. dubliniensis biofilms were inhibited by purpurin, a natural anthraquinone pigment isolated from madder root. Purpurin inhibited C. dubliniensis biofilm formation in a concentration-dependent manner; while mature biofilms were less susceptible to purpurin. Scanning electron microscopy (SEM) analysis revealed scanty structure consisting of yeast cells in purpurin-treated C. dubliniensis biofilms. We sought to delineate the mechanisms of the anti-biofilm activity of purpurin on C. Dubliniensis. Intracellular ROS levels were significantly elevated in fungal biofilms and depolarization of MMP was evident upon purpurin treatment in a concentration-dependent manner. DNA degradation was evident. However, no activated metacaspase could be detected. Together, purpurin triggered metacaspase-independent apoptosis in C. dubliniensis biofilms.

Calcineurin is required for pseudohyphal growth, virulence, and drug resistance in Candida lusitaniae

Candida lusitaniae is an emerging fungal pathogen that infects immunocompromised patients including HIV/AIDS, cancer, and neonatal pediatric patients. Though less prevalent than other Candida species, C. lusitaniae is unique in its ability to develop resistance to amphotericin B. We investigated the role of the calcium-activated protein phosphatase calcineurin in several virulence attributes of C. lusitaniae including pseudohyphal growth, serum survival, and growth at 37°C. We found that calcineurin and Crz1, a C. albicans Crz1 homolog acting as a downstream target of calcineurin, are required for C. lusitaniae pseudohyphal growth, a process for which the underlying mechanism remains largely unknown in C. lusitaniae but hyphal growth is fundamental to C. albicans virulence. We demonstrate that calcineurin is required for cell wall integrity, ER stress response, optimal growth in serum, virulence in a murine systemic infection model, and antifungal drug tolerance in C. lusitaniae. To further examine the potential of targeting the calcineurin signaling cascade for antifungal drug development, we examined the activity of a calcineurin inhibitor FK506 in combination with caspofungin against echinocandin resistant C. lusitaniae clinical isolates. Broth microdilution and drug disk diffusion assays demonstrate that FK506 has synergistic fungicidal activity with caspofungin against echinocandin resistant isolates. Our findings reveal that pseudohyphal growth is controlled by the calcineurin signaling cascade, and highlight the potential use of calcineurin inhibitors and caspofungin for emerging drug-resistant C. lusitaniae infections.

In vitro activity of echinocandins against non-Candida albicans: is echinocandin antifungal activity the same?

The echinocandins anidulafungin, caspofungin, and micafungin have a broad and similar spectrum of in vitro and in vivo activity against most Candida spp. Minimal inhibitory concentrations (MICs) for Candida spp. are usually below 1 μg/mL for most isolates. The exceptions are Candidaparapsilosis and C. guilliermondii. Species-specific clinical breakpoints (CBPs) and epidemiologic cutoff values (ECVs) have been proposed by the Clinical and Laboratory Standards Institute (CLSI) for the eight most common Candida spp. versus each echinocandin; these values are useful to detect in vitro antifungal resistance (CBPs) and to identify isolates harboring fks mutations or having reduced susceptibility (ECVs). This paper presents a review of the literature (2006-2010) regarding the in vitro activity similarities or differences among the three echinocandins against Candida spp.; different parameters or measurements of in vitro potency were evaluated. The focus of the review is the non-Candida albicans species.

[Scientific evidence supporting the use of micafungin in the treatment of invasive candidiasis]

Micafungin is a semisynthetic lipopeptide developed from Coleophoma empetri, which blocks the synthesis of β-1,3-D-glucan, an essential component of the fungal wall, though non-competitive inhibition of β-1,3-D-glucan synthetase. Micafungin is a dose-dependent candidacidal agent with excellent in vitro efficacy against most Candida spp. including species resistant to amphotericin B, such as Candida lusitaniae, several azoles, such as C. glabrata or C. krusei, and isolates not susceptible to other echinocandins. Moreover, this drug is active against Candida biofilms. Micafungin is a first-line drug for the treatment of candidemias and invasive candidiasis in adults and children (including neonates). This drug is approved for use in the treatment of invasive candidiasis and Candida esophagitis, as well as in the prophylaxis of Candida infections in hematopoietic stem cell transplant recipients or those at risk of prolonged neutropenia. Micafungin can be used both in the treatment and prevention of candidiasis in neonates, children, adolescents, adults, and the elderly, making it highly useful in patient groups in which the use of other antifungal drugs has not been authorized.

Antimycotic effect of the essential oil of Aloysia triphylla against Candida species obtained from human pathologies

The research of alternative substances to treat infections caused by Candida species is a need. Aromatic plants have the ability to produce secondary metabolites, such as essential oils (EO). The antimicrobial properties of Aloysia triphylla (L'Her.) Britton (cedrón) EO has been previously described. The aims of this work were to determine the antimicrobial activity and the effect on the cell structure of the EO of A. triphylla against Candida sp isolated from human illnesses. The EO was obtained by hydrodistillation of A. triphylla leaves. The minimum inhibitory concentration (MIC) was performed with microdilution method and the minimum fungicidal concentration (MFC) was determined. A. triphylla EO's showed antifungal activity against all yeast: C. albicans, C. dubliniensis, C. glabrata, C. krusei, C. guillermondii, C. parapsilosis and C. tropicalis which were resistant to fluconazol (150 mg/mL). The range of MIC values was from: 35 to 140 microg/mL and the MFC: 1842 to 2300 microg/mL. The time of killing at the MFC against C. albicans (3 x 10(5) UFC/mL) was 140 min. The dates of OD620 and OD260 suggest lysis and loss of absorbing material, respectively. The HROM shows distortion in morphology and shape of the cell, with large vacuoles in the cytoplasm. These studies clearly show that A. triphylla EO is a promising alternative for the treatment of candidiasis.

Using the residue of spirit production and bio-ethanol for protein production by yeasts

The residue (vinasse) formed during the distillation of bio-ethanol and cachaça, a traditional rum-type spirit produced from sugar-cane in Brazil, is highly harmful if discharged into the environment due to high values of COD and BOD. One possibility for minimizing the impact of vinasse in soils and waters is to use the residue in the production of microbial biomass for use as an animal feed supplement that will provide high levels on nitrogen (>9% d.m.) and low content of nucleic (≤ 10% d.m.) This paper reports the production and quality of biomass produced from fermentation of Saccharomyces cerevisiae and Candida parapsilosis in culture media under 12 different culture conditions and the respective effects of each variable (glucose, yeast extract, peptone, potassium phosphate, vinasse, pH and temperature). Of the S. cerevisiae isolates tested, two (VR1 and PE2) originating from fuel alcohol-producing plants were identified as offering the best potential for the industrial production of single cell protein from vinasse due to highest biomass productivity. Our results showed a potential viable and economic use of vinasse.

Effect of marine polyunsaturated fatty acids on biofilm formation of Candida albicans and Candida dubliniensis

The effect of marine polyunsaturated fatty acids on biofilm formation by the human pathogens Candida albicans and Candida dubliniensis was investigated. It was found that stearidonic acid (18:4 n-3), eicosapentaenoic acid (20:5 n-3), docosapentaenoic acid (22:5 n-3) and docosahexaenoic acid (22:6 n-3) have an inhibitory effect on mitochondrial metabolism of both C. albicans and C. dubliniensis and that the production of biofilm biomass by C. dubliniensis was more susceptible to these fatty acids than C. albicans. Ultrastructural differences, which may be due to increased oxidative stress, were observed between treated and untreated cells of C. albicans and C. dubliniensis with formation of rough cell walls by both species and fibrillar structures in C. dubliniensis. These results indicate that marine polyunsaturated fatty acids may be useful in the treatment and/or prevention of biofilms formed by these pathogenic yeasts.

Scanning electron and confocal scanning laser microscopy imaging of the ultrastructure and viability of vaginal Candida albicans and non- albicans species adhered to an intrauterine contraceptive device

Although bacterial biofilms have been studied in detail, adhesion of Candida albicans and non-albicans species to an intrauterine contraceptive device (IUD) is not clear. The objective of this study was to evaluate aspects of imaging of the ultrastructure and viability of vaginal yeasts adhered to different parts of an IUD, through scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). We studied yeasts isolated from different patients with vulvovaginal candidiasis: C. albicans, C. glabrata, C. guillermondii, C. parapsilosis, C. tropicalis, and Saccharomyces cerevisiae. A suspension of the each yeast was prepared and incubated with IUD parts (tail, without copper, and copper-covered). SEM and CSLM showed that all the vaginal yeasts adhered to all the parts of the IUD and demonstrated viability, including 30 days after contact for C. albicans. Possibly irregularities of IUD surface contribute to the adherence process. Although all of the IUD parts contribute to retention of yeasts in the genital tract, high concentration of yeast cells on the tail may indicate the importance of this segment in maintaining the colonization by yeast cells because the tail forms a bridge between the external environment, the vagina that is colonized by yeast cells, and the upper genital tract where there is no colonization.

Genetic basis of Candida biofilm resistance due to drug-sequestering matrix glucan

Medical devices provide an ecological niche for microbes to flourish as a biofilm community, protected from antimicrobials and host defenses. Biofilms formed by Candida albicans, the most common fungal pathogen, survive exposure to extraordinarily high drug concentrations. Here, we show that beta-glucan synthase Fks1p produces glucan, which is deposited in the biofilm matrix. The extracellular glucan is required for biofilm resistance and acts by sequestering antifungals, rendering cells resistant to their action. These findings provide the genetic basis for how biofilm matrix production governs drug resistance by impeding drug diffusion and also identify a useful biofilm drug target.

Antifungal activity of the essential oil of Thymus x viciosoi against Candida, Cryptococcus, Aspergillus and dermatophyte species

The essential oil (EO) of Thymus x viciosoi (Pau) R. Morales was isolated and analysed by GC and GC-MS. The antifungal activity of the EO and its major components against clinically relevant yeasts and molds was then measured. Their influence on the germ tube formation in Candida albicans and the influence of the EO on the metabolic function and cytoplasmic membrane integrity in the same yeast, analyzed by flow cytometry, were also studied. The EO showed high contents of carvacrol, thymol, and P-cymene. The total EO, as well as its components carvacrol and thymol, displayed very low minimum inhibitory concentrations and minimum fungicidal concentrations against all tested organisms (0.04 to 0.64 microL mL(-1)), while P-cymene showed weaker activity (2.5 to > 20.0 microL mL(-1)). They also inhibited filamentation at sub-inhibitory concentrations in C. albicans, particularly P-cymene, and the EO led to rapid metabolic arrest, disruption of the plasma membrane and consequently cell death. The EO and its main components were found to display a broad fungicidal activity through the disruption of cytoplasmic membrane integrity leading to leakage of vital intracellular compounds. In conclusion, the phenolic oil of T. x viciosoi may have potential for use in the development of clinically useful antifungal preparations.

Improvement of chromium biosorption by UV-HNO(2) cooperative mutagenesis in Candida utilis

The present study focused on the improvement of chromium resistance and biosorption efficiency in Candida utilis CR-001 utilizing protoplast mutagenesis technology. Through ultraviolet (UV) radiation, HNO(2) treatment and chromium acclimatization, six preferred mutants of C. utilis CR-001 were screened out, namely, CRU132-26, CRC7-2, CRC2811-1, CRC2811-2, CRC2814-8 and CRY182-1. The removal efficiency of these mutants for 20mg/L Cr(VI) solutions were 85.6%, 95.2%, 87.0%, 82.5%, 94.7% and 82.7%, respectively, noticeably greater than that of the parent strain CR-001 (79.5%). Furthermore, CRC2811-1 exhibited outstanding application potential with high removal efficiency and low dosage over a wide range of pH. Cell surface and inner details of CRC2811-1 and its parent strain CR-001 were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in order to explore possible changes caused by inducement. The results showed that Cr-sorption of CR-001 mainly depended on intracellular accumulation, but for CRC2811-1, cell surface deposition was also involved in improving its chromium biosorption capacity.

Sub-100 nm IR spectromicroscopy of living cells

We have performed IR spectromicroscopy of cells immersed in liquid water, with a lateral resolution better than 100 nm. Here, we use the motion of an atomic force microscope tip, probing the local transient deformation induced by an IR pulsed laser tuned at a sample absorbing wavelength. By Fourier analysis of the vibration of the cantilever tip, we can discriminate frequencies that are characteristic of the object, thus eliminating the influence of the water absorption. This opens the door of chemical imaging of living species in vivo, with spatial resolution of the order of the size of cell components.

In vitro biofilm formation of Candida albicans and non-albicans Candida species under dynamic and anaerobic conditions

An understanding of biofilm behavior of Candida species under different environmental conditions is key to the development of effective preventive measures for candidal infections. Hence in this study we assessed the impact of the environmental milieu on Candida biofilm formation using polystyrene, flat-bottomed 96-well microtiter plates. A total of 20, comprising 10 clinical isolates each of Candida albicans and, non-albicans species of Candida were compared for their biofilm forming ability both under aerobic and anaerobic conditions, and static and dynamic conditions. XTT reduction assay was used to quantify the sessile growth. Biofilm formation of all 10 C. albicans isolates differed significantly between dynamic and static states under both atmospheric conditions (P<0.05). For non-albicans Candida species, a significant difference in biofilm growth between dynamic and static states was noted only when incubated aerobically (P<0.05), and no significant difference in biofilm formation was noted between aerobic and anaerobic conditions. Scanning electron microscopy revealed that C. albicans produced a compact multilayered biofilm embedded in noticeably higher quantity of extracellular polymeric matrix in aerobic/dynamic conditions compared with anaerobic/static conditions. Our data indicate that biofilm formation of C. albicans and non-albicans Candida species is modulated by hydrodynamic conditions and ambient oxygen gradients. However, further work is required to fully elucidate how Candida biofilms persist within the oral milieu under such challenging ecological pressures.

Enhancement of the in vitro activity of amphotericin B against the biofilms of non-albicans Candida spp. by rifampicin and doxycycline

The in vitro activity of amphotericin B (AMB) alone and in combination with rifampicin (RIF) and doxycycline (DOX) was tested against the biofilms of 30 clinical isolates of non-albicans Candida (NAC) species namely, Candida parapsilosis, Candida krusei and Candida glabrata. The killing activity of AMB at 10 x MIC was significantly increased in combination with either antibiotic. With RIF, the killing activity increased by 20.6, 23.5 and 14 % against the biofilms of C. parapsilosis, C. krusei and C. glabrata, respectively; with DOX, the killing activity increased by 30.64, 35.28 and 31.13 %, respectively. Pre-exposure of the isolates to the same combinations significantly reduced the number of colonized cells in the biofilms by 20, 25.14 and 13.07 % with RIF for C. parapsilosis, C. krusei and C. glabrata, respectively, and by 18.94, 24.52 and 29.15 % with DOX, respectively. The data showed that combination of RIF or DOX with AMB enhanced the killing activity of the antifungal agent against biofilms of NAC species. Whether such an effect operates against biofilm-associated infections needs to be clarified by further in vivo studies.

Candida hyderabadensissp. nov., a novel ascomycetous yeast isolated from wine grapes

Three ascomycetous yeast strains were isolated from decaying green wine grapes, collected from Hyderabad city in India. Two strains, YS9 and YS21, were identified as Kodamaea ohmeri and Candida fermentati, respectively. The third strain, YS12(T), differs from Candida parapsilosis, Candida orthopsilosis and Candida metapsilosis, the nearest phylogenetic neighbours, by 1.6-1.9% with respect to the nucleotide sequence of the D1/D2 domain of the 26S rRNA gene and by 1.4-9.2% with respect to the nucleotide sequence of the internal transcribed spacer 1 (ITS1)-5.8S rRNA gene-ITS2 region. YS12(T) also differs from C. parapsilosis, C. metapsilosis and C. orthopsilosis by some phenotypic characteristics. Thus, based on the phenotypic differences and phylogenetic analysis, strain YS12(T) is assigned the status of a new species of Candida, for which the name C. hyderabadensis sp. nov. is proposed. The type strain is YS12(T) (NRRL Y-27953(T)=CBS10444(T)=IAM15334(T)).

[Useful phenotypic characteristics for presumptive identification of Candida guilliermondii]

Candida guilliermondii developed a pink-purplish colony on CHROMagar Candida. In the micromorphology in milk-tween 80 1% agar at 28 degrees C after 48 h of incubation C. guilliermondii showed small (3-5 microm), spherical yeasts without pseudohyphaes. This Candida species presented a characteristic cluster of blastospores with pseudohyphaes radiating from the centre at 96 h. The trehalose-sucrose assimilation assay was applied to the C. guilliermondii isolates which proved negative for trehalose and positive for sucrose. These results allowed for the presumptive identification of C. guilliermondii. The results were concordant in 100% of the isolates with the identification of the C. guilliermondii species by the ID 32C and Vitek YBC methods. Such automated methods offered Candida famata as a second option, with a reliability percentage of 10%. Micromorphological studies increase yeast identification reliability, especially among species presenting similar biochemical profiles.

Candida kazuoi sp. nov. and Candida hasegawae sp. nov., two new species of ascomycetous anamorphic yeasts isolated from insect frass in Thailand

Two strains of anamorphic yeasts isolated from insect frass collected in southern Thailand were assigned to the genus Candida based on the conventional taxonomic criteria used for yeast classification. In the phylogenetic tree based on the D1/D2 domain of the 26S rDNA, these strains are distant from the known species of yeasts and considered to represent two different new species. They are named Candida kazuoi sp. nov. and Candida hasegawae sp. nov.

[Candida dubliniensis: need for correct diagnosis]

A study of 115 strains, which had been isolated from vaginal smears and identified at the beginning as Candida albicans, was conducted to find out if there was Candida dubliniensis in Cuba. The growth of those isolates that due to their morphological characteristics were identifified as either C. albicans or C. dubliniensis was checked up at 42 degrees in Sabouraud agar. C. albicans was the predominant species (88.69%). For the first time in Cuba, 13 C. dubliniensis strains were presumptively identified. The achieved results are of great benefit because they will contribute to the conduction of epidemiological and resistance studies to antifungicidal products.

Interspecies variation in Candida biofilm formation studied using the Calgary biofilm device

An in vitro assay to study multiple Candida biofilms, in parallel, has been carried out using the Calgary biofilm device (CBD). We here report: i) standardization of the CBD for Candida albicans biofilm formation, ii) kinetics of C. albicans biofilm formation, iii) biofilm formation by five Candida species, and iv) effect of dietary carbohydrates on biofilm formation. The biofilm metabolic activity on all CBD pegs was similar (p=0.6693) and C. albicans biofilm formation revealed slow growth up to 36 h and significantly higher growth up to 48 h (p<0.001). Significant differences in total biofilm metabolic activity were seen for glucose, fructose and lactose grown C. albicans compared with sucrose and maltose grown yeasts. Candida krusei developed the largest biofilm mass (p<0.05) relative to C. albicans, C. glabrata, C. dubliniensis and C. tropicalis. Scanning electron microscopy revealed that C. krusei produced a thick multilayered biofilm of pseudohyphal forms embedded within the polymer matrix, whereas C. albicans, C. dubliniensis and C. tropicalis biofilms consisted of clusters or chains of cells with sparse extracellular matrix material. We conclude that CBD is a useful, simple, low cost miniature device for parallel study of Candida biofilms and factors modulating this phenomenon.

Isolation and characterization of a 30 kD antifungal protein from seeds of Sorghum bicolor

An antifungal protein of about 30,000 Da was isolated from seeds of Sorghum bicolor L. using chromatographic techniques, including gel filtration, ion exchange, and high-performance liquid chromatography in a reverse-phase column. This protein (termed 30 kD protein) showed a minimal inhibitory concentration of 36 microg/ml for Candida parapsilosis and C. tropicalis, and 18 microg/ml for C. albicans. The 30 kD protein inhibited adherence to the cover glass and formation of a germinative tube of C. albicans at concentrations over 300 and 150 microg/ml, respectively. Transmission electron microscopy of yeast forms of C. albicans after incubation with 18 mug/ml of the 30 kD protein for 24 h revealed marked ultrastructural changes in the fungus. No toxicity of the 30 kD protein to the culture of Hep2 cells at concentrations equal to or less than 1,000 microg/ml was observed.

Ultrastructural and physico-chemical heterogeneities of yeast surfaces revealed by mapping lateral-friction and normal-adhesion forces using an atomic force microscope

Scanning force microscopy has been used to probe the surface of the emerging pathogenic yeast Candida parapsilosis, in order to get insight into its surface structure and properties at submicrometer scales. AFM friction images eventually show patches with a very strong contrast, showing high lateral interaction with the tip. Adhesion force measurement also reveals a high normal interaction with the tip, and patches show extraordinarily high pull off values. The tip eventually sticks completely at the center of the patches. While an extraordinarily high interaction is measured by the tip at those zones, topographic images show extraordinarily flat topography over those zones, both of which characteristics are consistent with a liquid-like area. High resolution friction images show those zones to be surrounded by microfibrillar structures, concentrically oriented, of a mean width of about 25 nm, structures that become progressively less defined as we move away from the center of the patches. No structure can be appreciated inside the zones of maximum contrast. Also some helical or ribbon-like structure can be resolved from friction images. There is not only an ordered disposition of the microfibrillar structures, but also the adhesion force increases radially in the direction towards the center of the patches. These structures responsible for the high adhesion are thought to be incipient-emerging budding zones. Microfibrillar structures are thought to represent the first steps of chitin biosynthesis and cell wall digestion, with chitin polymers being biosynthesized, associated with other macromolecules of the yeast cell wall. They can be also beta glucan helical structures, made visible in the zone of yeast division due to the action of autolysins. The observed gradient in surface adhesion and elastic properties correlates well with that expected from a biochemical point of view. The higher adhesion force measured could be either due to the different macromolecular nature of the patches, or to a mechanical adhesion effect due to the different plasticity of that zone. This work reveals the importance of taking into account the dynamic nature of the cell wall physico-chemical properties. Processes related to the normal cell-cycle, as division, can strongly alter the surface morphology and physico-chemical properties and cause important heterogeneities that might have a profound impact on the adhesion behavior of a single cell, which could not be detected by more macroscopic methods.

Inhibitory activity of 2-deoxy-D-glucose and Candida saitoana against Penicillium digitatum

The toxic activity of 2-deoxy-D-glucose (2-DG) alone or combined with the biocontrol yeast Candida saitoana strain 8C was evaluated in vitro and in vivo against the postharvest fungal pathogen Penicillium digitatum. In order to assess the effect of the 2-DG on both the biocontrol yeast and fungal pathogen, in vitro tests were performed in Petri dishes containing potato dextrose agar amended with different concentrations (1.5, 3.0, 6.0, 15.0, 30.0, 60.0 mM) of the sugar. The plates were then seeded with 25 microl of a P. digitatum conidial suspension at 10(5) conidia/mL. Result of the assays showed an enhanced inhibitory activity as concentration increased from 15.0 to 60.0 mM. Corroborated by SEM observations showing a reduced growth and the appearance of damaged hyphae were found. At 60 mM of 2-DG, a total inhibition occurred while concentrations from 1.5 to 6.0 mM resulted ineffective. The same tests evidenced no adverse effects on the yeast 8C at all tested concentrations. In vivo assays were carried out on orange fruit cv 'Biondo comune', wounded in 5 sites around the calyx. Each wound (2.5 wide and 3.4 mm depth) was first filled with 25 microl of a 0, 3.0, 6.0, 15.0, 30.0 or 60.0 mM 2-DG-water solution alone or combined with the yeast 8C at 10(8) cells/mL and then a 25 microl of the P. digitatum conidial suspension was added. Each treatment consisted of 3 replicates of 8 fruit (5 wounds/fruit) for a total 120 wounds per treatment. Oranges were maintained at 20 degrees C and high RH (95-98%) for up to 5 days, during which infection was monitored and the inhibitory activity calculated. The tests in vitro evedenced a significant slowing of the pathogen growth with the highest concentrations of 2-DG (15.0, 30.0 and 60.0 mM) with respect to the control; while at lower concentrations (1.5, 3.0, 6.0 mM) the development of the fungi was not significantly reduced. C. saitoana was resistant to all the doses employed to the abovementioned compound. In vivo the yeast alone was more effective compared to the sugar alone up to 6.0 mM while, at higher concentrations an additive effect was founded.

The closely related species Candida albicans and Candida dubliniensis can mate

Because Candida dubliniensis is closely related to Candida albicans, we tested whether it underwent white-opaque switching and mating and whether white-opaque switching depended on MTL homozygosity and mating depended on switching, as they do in C. albicans. We also tested whether C. dubliniensis could mate with C. albicans. Sequencing revealed that the MTLalpha locus of C. dubliniensis was highly similar to that of C. albicans. Hybridization with the MTLa1, MTLa2, MTLalpha1, and MTLalpha2 open reading frames of C. albicans further revealed that, as in C. albicans, natural strains of C. dubliniensis exist as a/alpha, a/a, and alpha/alpha, but the proportion of MTL homozygotes is 33%, 10 times the frequency of natural C. albicans strains. C. dubliniensis underwent white-opaque switching, and, as in C. albicans, the switching was dependent on MTL homozygosis. C. dubliniensis a/a and alpha/alpha cells also mated, and, as in C. albicans, mating was dependent on a switch from white to opaque. However, white-opaque switching occurred at unusually high frequencies, opaque cell growth was frequently aberrant, and white-opaque switching in many strains was camouflaged by an additional switching system. Mating of C. dubliniensis was far less frequent in suspension cultures, due to the absence of mating-dependent clumping. Mating did occur, however, at higher frequencies on agar or on the skin of newborn mice. The increases in MTL homozygosity, the increase in switching frequencies, the decrease in the quality of switching, and the decrease in mating efficiency all reflected a general deterioration in the regulation of developmental processes, very probably due to the very high frequency of recombination and genomic reorganization characteristic of C. dubliniensis. Finally, interspecies mating readily occurred between opaque C. dubliniensis and C. albicans strains of opposite mating type in suspension, on agar, and on mouse skin. Remarkably, the efficiency of interspecies mating was higher than intraspecies C. dubliniensis mating, and interspecies karyogamy occurred readily with apparently the same sequence of nuclear migration, fusion, and division steps observed during intraspecies C. albicans and C. dubliniensis mating and Saccharomyces cerevisiae mating.

Candida riodocensis and Candida cellae, two new yeast species from the Starmerella clade associated with solitary bees in the Atlantic rain forest of Brazil

Two new ascomycetous yeast species belonging to the Starmerella clade were discovered in nests of two solitary bee species in the Atlantic rain forest of Brazil. Candida riodocensis was isolated from pollen-nectar provisions, larvae and fecal pellets of nests of Megachile sp., and Candida cellae was found in pollen-nectar provisions of Centris tarsata. Analysis of the sequences of the D1/D2 large-subunit ribosomal DNA showed that C. riodocensis is phylogenetically related to C. batistae, and the closest relative of C. cellae is C. etchellsii. The type strains are C. riodocensis UFMG-MG02 (=CBS 10087(T) = NRRL Y-27859(T)) and C. cellae UFMG-PC04 (=CBS 10086(T) = NRRL Y-27860(T)).

Detection of Helicobacter pylori-specific genes in the oral yeast

BACKGROUND

Until today, human stomach is the only recognized habitat of Helicobacter pylori. However, recruitment of DNA-based methods has made possible the detection of H. pylori in water and oral cavity, thus suggesting fecal-oral and oral-oral routes for transmission of H. pylori, respectively. In this study, yeast has been proposed as a common vector for transmission of H. pylori. Thus designed primers were recruited to target 16S rDNA and cagA genes in the oral yeasts by PCR.

MATERIALS AND METHODS

Eighteen yeasts were examined microscopically for the presence of bacterial-like bodies. DNAs were extracted from oral yeasts using phenol-chloroform method. Amplification conditions were optimized as 33 cycles and annealing temperatures of 63 degrees C for 16S rDNA and 51 degrees C and 52 degrees C for cagA gene which was targeted in two steps. DNAs of H. pylori and Saccharomyces cerevisiae were used as controls. Polymerase chain reaction (PCR) products of two genes from one yeast and from H. pylori were cloned in pCAP and subsequently subcloned in pSK+ and were sequenced.

RESULTS

Bacterial-like bodies were observed in all oral yeasts. The amplified products of 16S rDNA from all oral yeasts were homologous in size with those of H. pylori. Fifteen out of eighteen (83%) yeasts contained cagA gene, homologous to H. pylori. CagA was not amplified from three yeasts and S. cerevisiae. Analysis of the sequenced products of 16S rDNA and cagA from one oral yeast showed 98% homology with those of H. pylori.

CONCLUSIONS

The presence of H. pylori inside the yeast was indicated by light microscopy and PCR. It appears that yeasts, which are abundant in nature and thrive the mucosal surfaces of human, might serve as reservoirs and vehicles of H. pylori.

In vitro method to study antifungal perfusion in Candida biofilms

Antimycotic perfusion through Candida biofilms was demonstrated by a modification of a simple in vitro diffusion cell bioassay system. Using this model, the perfusion of three commonly used antifungal agents, amphotericin B, fluconazole, and flucytosine, was investigated in biofilms of three different Candida species (i.e., Candida albicans, Candida parapsilosis, and Candida krusei) that were developed on microporous filters. Scanning electron microscopy revealed that C. albicans formed a contiguous biofilm with tightly packed blastospores and occasional hyphae compared with C. parapsilosis and C. krusei, which developed confluent biofilms displaying structural heterogeneity and a lesser cell density, after 48 h of incubation on nutrient agar. Minor structural changes were also perceptible on the superficial layers of the biofilm after antifungal perfusion. The transport of antifungals to the distal biofilm-substratum interface was most impeded by C. albicans biofilms in comparison to C. parapsilosis and C. krusei. Fluconazole and flucytosine demonstrated similar levels of perfusion, while amphotericin B was the least penetrant through all three biofilms, although the latter appeared to cause the most structural damage to the superficial cells of the biofilm compared with the other antifungals. These results suggest that the antifungal perfusion through biofilm mode of growth in Candida is dependent both on the antimycotic and the Candida species in question, and in clinical terms, these phenomena could contribute to the failure of Candida biofilm-associated infections. Finally, the in vitro model we have described should serve as a useful system to investigate the complex interactions that appear to operate in vivo within the biofilm-antifungal interphase.

Simple and reliable detection of slime production of Candida spp. directly from blood culture bottles: comparison of visual tube method and transmission electron microscopy

Early detection of slime production may be useful for clinical decision because of its suggestive property for potential pathogenic capacity of a Candida strain especially in patients with a prosthetic device. In this study we aimed to compare the visual tube method (VTM) with transmission electron microscopy (TEM) in order to confirm the reliability of the former method. In order to demonstrate the reproducibility of the tube method and to determine the correct timing for the test, Candida isolates directly obtained from blood culture (DBC) bottles and their two subsequent subcultures were used. The results of this study showed that VTM is a simple and reliable method which can be used in every clinical mycology laboratory, provided that the test is applied on DBC isolates; as the ability of slime production is decreased or lost even after the first subculturing. We suggest that this simple method can be used and may have some contributions to the ongoing studies on the controversial issue concerning removal of biomaterials in candidemic patients.

Plasma Membrane Alteration Is an Early Signaling Event in Doxorubicin-Induced Apoptosis in the YeastCandida utilis

Signaling pathways such as increased ceramide, mitochondrial dysfunction, and P3 and caspase activation are produced by anticancer drugs and lead to apoptosis. In this research we show that the first event after culturing the yeast Candida utilis in the presence of low doses of doxorubicin (25 microg/mL) is the morphological alteration of the plasma membrane. In the presence of higher doxorubicin doses (>/=50 microg/mL), in addition to profound alterations in the plasma membrane, changes in mitochondrial shape and cristae organization were observed. Concomitantly, increases in respiration, substrate oxidation, and cytochrome biosynthesis were observed at low doxorubicin doses (up to 25 microg/mL), whereas a progressive decrease was observed at higher doses. [(3)H]Leu incorporation into proteins increased by 40% in the mitochondrial fraction and by 19% in the cytosol in the presence of 25 microg/mL doxorubicin; it decreased to 80% of the control in the cytosol in the presence of 1 mg/mL doxorubicin. Morphologically, doxorubicin doses of up to 200 microg/mL produced apoptosis, whereas higher doxorubicin doses produced necrosis.

In vitro activity of essential oil from Ocimum gratissimum L. against four Candida species

Development of effective strategies for treatment of candidiasis and other fungal diseases has posed a challenge, considering the increase in opportunistic fungal infections in HIV-positive and immunocompromised patients. The in vitro antifungal activity of essential oil from Ocimum gratissimum was investigated in order to evaluate its efficacy against Candida albicans, Candida krusei, Candida parapsilosis, and Candida tropicalis. Transmission and scanning electron microscopy and negative staining in light microscopy were performed to reveal the effects of the essential oil on the morphology of these yeasts. Determination of minimal inhibitory concentrations and time-kill curves demonstrated that the essential oil showed fungicidal activity against all of the Candida species studied. Analysis of the ultrastructure of the yeast cells revealed changes in the cell wall and in the morphology of some subcellular organelles. Bud formation in the yeasts was impaired in treated cells. The essential oil of O. gratissimum is a potential candidate as a phytotherapeutic agent in some fungal diseases and for the control of fungi in the environment.

Uptake of chromium(III) and chromium(VI) compounds in the yeast cell structure

The study presented in this article investigated the influence of different Cr(III) and Cr(VI) compounds in the cultivation medium on the uptake and localization of chromium in the cell structure of the yeast Candida intermedia. The morphology of the yeast cell surface was observed by the scanning electron microscopy. Results demonstrated that the growth inhibitory concentration of Cr(III) in the cultivation medium induced changes in the yeast cell shape and affected the budding pattern, while inhibitory concentration of Cr(VI) did not cause any visible effects on morphological properties of the yeast cells. The amount of total accumulated chromium in yeast cells and the distribution of chromium between the yeast cell walls and spheroplasts were determined by atomic absorption spectroscopy. No significant differences were found neither in total chromium accumulation nor in the distribution of chromium in yeast cell walls and spheroplasts between the two of Cr(VI) compounds. Conversely, substantial differences between Cr(III) compounds were demonstrated in the total uptake as well as the localization of chromium in yeast cells.

[Phenotypic evaluation to differentiate Candida albicans from Candida dubliniensis]

This study evaluated the phenotypic tests used to differentiate Candida albicans from Candida dubliniensis. A total of 55 isolates from vaginal secretions, oral cavity and hemoculture were studied. They were originally identified as C. albicans, based on their morphological and physiological characteristics. These isolates were tested for colony color development on CHROMagar Candida medium, growth at 45 degrees C on Sabouraud Dextrose agar, lipolytic activity on Tween 80 Agar medium and colony morphology and chlamydoconidia formation on Staib agar medium. Of the 55 isolates studied, seven yielded one or more phenotypic characteristics suggestive of Candida dubliniensis. These isolates were tested by PCR with specific primers for Candida dubliniensis and API ID 32. The seven isolates were confirmed as Candida albicans. All of these finding indicate that DNA based tests should be used for definitive identification of Candida dubliniensis.

Candida and Candidiasis: The Cell Wall as a Potential Molecular Target for Antifungal Therapy

The fungal species Candida albicans is an opportunistic pathogen, which causes serious infections in humans, particularly in immunocompromised patients. Depending on the underlying host defect, C. albicans causes a variety of infections, ranging from superficial mucocutaneous candidiasis to life-threatening disseminated infections. Both the limited spectrum of antifungal drugs currently in clinical use and the emergence of resistances make necessary the development of new effective antifungal drugs with minimal side effects; however, such a research is limited by the small number of specific target sites identified to date. The cell wall is a fungal specific dynamic structure essential to almost every aspect of the biology and pathogenicity of C. albicans. Its structure confers physical protection and shape to fungal cells, and as the most external part of the fungus, the cell wall mediates the interaction with the host, including adhesion to host tissues and modulation of the host anti-Candida immune response. Consequently, the fungal cell wall can be considered as a suitable target for development of new antifungal compounds. Therefore two distinct types of potential cell wall-related targets can be envisaged, according to their mode of action in inhibiting infection: (i) inhibition of cell wall biogenesis, which may impair cell wall integrity and thus cell viability, and (ii) modification of host-fungus interactions by inhibiting or blocking putative virulence factors, which may impair host colonization and progress of the infectious process. Antibodies specific to cell wall antigens may protect against infection by a variety of mechanisms and may evolve into save antifungal agents.

Relationship between the morphology of Candida cells and vaginal discharge

The aim of this study was to detect whether there is a correlation between the dimorphic pattern of Candida cells and various types of vaginal discharge. For this purpose, 2861 Papanicolaoustained cervicovaginal smears were examined cytologically and 265 of 2861 (9.26%) were diagnosed as having Candida cells. The 88 of 295 (29.83%) were identified as having blastospores only, 135 of 295 (45.76%) as having "hyphae only", and 47 of 295 (15.93%) as having both blastospores and hyphae of candida cells. There was a significant correlation between the type of candida cells and vaginal discharge (p < 0.05). The white-cheesy type vaginal discharge was the most prominent symptom for the observation the "hyphae only" following "blastospores only" and both blastospores and hyphae of Candida cells. It was suggested that hyphael form of Candida cells is the most pathogenic pattern and white-cheesy vaginal discharge is a marker for the presence of hyphael form in the vaginal mucosa.

Candida bombicola Cells Immobilized on Patterned Lipid Films as Enzyme Sources for the Transformation of Arachidonic Acid to 20-HETE

Preparation of biocompatible surfaces for immobilization of enzymes and whole cells is an important aspect of biotechnology due to their potential applications in biocatalysis, biosensing, and immunological applications. In this report, patterned thermally evaporated octadecylamine (ODA) films are used for the immobilization of Candida bombicola cells. The attachment of the cells to the ODA film surface occurs possibly through nonspecific interactions such as hydrophobic interactions between the cell walls and the ODA molecules. The enzyme cytochrome P450 present in the immobilized yeast cells on the ODA film surface was used for the transformation of the arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE). The assembly of cells on the hydrophobic ODA surface was confirmed by quartz crystal microgravimetry (QCM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). SEM images confirmed the strong binding of the yeast cells to the ODA film surface after biocatalytic reactions. Moreover, the biocomposite films could be easily separated from the reaction medium and reused.

Yeast cell adhesion on oligopeptide modified surfaces

Self-assembling oligopeptides are novel materials with potential bioengineering applications; this paper explores the use of one of these oligopeptides, EAK 16 II, for modifying the surface properties of cell-supporting substrates. To characterize the surface properties, thermodynamic measurements of liquid contact angle and surface free energy were correlated to atomic force microscopy (AFM) observations. A critical concentration of 0.1 mg/ml was found necessary to completely modify the surface properties of the substrate with EAK 16 II. Adhesion of a yeast cell, Candida utilis, was modified by the coating of EAK 16 II on both hydrophobic (plastic) and hydrophilic (glass) surfaces: Cell coverage was slightly enhanced on the glass substrate, but decreased significantly on the plastic substrate. This indicates that the yeast cell adhesion was mainly determined via hydrophobic interactions between the substrate and the cell wall. However, on the EAK 16 II modified glass substrate, surface roughness might be a factor in causing a slightly larger cell adhesion than that on bare glass. The morphology of adhered cells was also obtained with AFM imaging, showing a depression at the center of the cell on all substrates. Small depressions on the oligopeptide-coated surfaces and plastic substrate may indicate good water-retaining ability by the cell. There was no apparent difference in cell adhesion and morphology among cells obtained from lag, exponential and stationary growth phases.

Fluorescence and Infrared Spectrometric Study of Cell Walls from Candida, Kluyveromyces, Rhodotorula and Schizosaccharomyces Yeasts in Relation with Their Chemical Composition

Composition, level, and arrangement of the structural polysaccharides determine biophysical properties of fungal cell walls. A small amount of a beta(1-->4) linear homopolymer of GlcNAc in the cell wall forms chitin. To study the components of the cell walls and to estimate the quantity of chitin for different strains, two spectroscopic methods were applied. Because chemical and enzymatic methods are destructive, long, and complex, fluorescence and infrared (IR) spectroscopies were applied on cell walls and on chitin enriched fractions. The results were compared to chemical assays. IR spectra allow identifying the structural types of polysaccharides in yeast walls. Fluorescence spectroscopy was not appropriated for a full and accurate quantitative determination of the polymers but revealed level variations similar to results obtained by chemical analytical methods. The infrared spectra, using a chemometric approach (PLS1), allowed a fairly good estimation of chitin in enriched fractions with respect to the chemical assays.

[Morphometric study of yeast cells of Torulopsis sphaerica after He-Ne-laser irradiation]

A study was made of structural organization of Torulopsis sphaerica cells irradiated with He-Ne (lambda = 632.8 nm; dose--460 J/m2) and then cultured in the nutrient with 1% glucose and O2 for 6 h. The computer analysis of electron images of cell sections was carried out. Evidences of stimulation of cell proliferation were found, including decrease in the areas of cell and chondriome profiles, decrease in the number of mitochondria on sections, elongation of cells and mitochondria, and increased variability of cell parameters. In addition, cells of irradiated cultured were characterized by the increase in the number of mitochondria contacting the endoplasmic reticulum (in this case the outer mitochondrial membrane presumably associates with the ER membrane), which may suggest the activation of ATP synthesis. Thus, He-Ne laser irradiation activates cell metabolism even at the early stage of culture growth.

Candida biofilms and their role in infection

Pathogenic fungi in the genus Candida can cause both superficial and serious systemic disease, and are now recognized as major agents of hospital-acquired infection. Many Candida infections involve the formation of biofilms on implanted devices such as indwelling catheters or prosthetic heart valves. Biofilms of Candida albicans formed in vitro on catheter material consist of matrix-enclosed microcolonies of yeasts and hyphae, arranged in a bilayer structure. The biofilms are resistant to a range of antifungal agents currently in clinical use, including amphotericin B and fluconazole, and there appear to be multiple resistance mechanisms. Recent studies with mixed biofilms containing Candida and bacterial species suggest that extensive and striking interactions occur between the prokaryotic and eukaryotic cells in these adherent populations.

[Architecture, influencing factors, and sensitivity to antifungal agents of Candida biofilm]

OBJECTIVE

To establish a model of Candida biofilm and to explore its characteristics, ultrastructure, influences by saliva and serum, and sensitivity to antifungal agents.

METHODS

Evaluations of the in vitro growth kinetics, influences by saliva and serum, and sensitivity to antifungal agents of Candida biofilm were performed with the abated tetrazolium salt XTT method on a 96-well microtire petri dish. The ultrastructure of Candida biofilm was observed under Confocal Laser Scanning Microscope (CLSM).

RESULTS

The bioactivity of Candida biofilm increased with culturing time and serum could obviously increase the action of biofilm. The Candida biofilm was significantly resistant to routine antifungal agents.

CONCLUSION

The Candida cells adhered in biofilms are significantly different in morphology from those in suspension and are resistant to routine antifungal agents such as Amphotericine B, Fluconazole and Itraconazole.

Antifungal susceptibility of Candida biofilms: unique efficacy of amphotericin B lipid formulations and echinocandins

Biofilms, likely the predominant mode of device-related microbial infection, exhibit resistance to antimicrobial agents. Evidence suggests that Candida biofilms have dramatically reduced susceptibility to antifungal drugs. We examined antifungal susceptibilities of Candida albicans and Candida parapsilosis biofilms grown on a bioprosthetic model. In addition to conventional agents, we determined if new antifungal agents (triazoles, amphotericin B lipid formulations, and echinocandins) have activities against Candida biofilms. We also explored effects of preincubation of C. albicans cells with subinhibitory concentrations (sub-MICs) of drugs to see if they could modify subsequent biofilm formation. Finally, we used confocal scanning laser microscopy (CSLM) to image planktonic- and biofilm-exposed blastospores to examine drug effects on cell structure. Candida biofilms were formed on silicone elastomer and quantified by tetrazolium and dry weight (DW) assays. Susceptibility testing of fluconazole, nystatin, chlorhexidine, terbenafine, amphotericin B (AMB), and the triazoles voriconazole (VRC) and ravuconazole revealed resistance in all Candida isolates examined when grown as biofilms, compared to planktonic forms. In contrast, lipid formulations of AMB (liposomal AMB and AMB lipid complex [ABLC]) and echinocandins (caspofungin [Casp] and micafungin) showed activity against Candida biofilms. Preincubation of C. albicans cells with sub-MIC levels of antifungals decreased the ability of cells to subsequently form biofilm (measured by DW; P < 0.0005). CSLM analysis of planktonic and biofilm-associated blastospores showed treatment with VRC, Casp, and ABLC resulted in morphological alterations, which differed with each agent. In conclusion, our data show that Candida biofilms show unique susceptibilities to echinocandins and AMB lipid formulations.