[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.