In vitro susceptibility of Candida species to lactoferrin

Lactoferrin is an antimicrobial protein present in human mucosal secretions as well as saliva. As there is no information on the relative fungicidal activity of human and bovine lactoferrin, an oral isolate of Candida albicans was studied for its susceptibility to these two proteins. Exposure to a concentration of 20 micrograms ml-1 of either HLF or BLF at 37 degrees C inactivated the yeast to the same degree irrespective of the incubation time of 45, 90 or 150 min. A similar study, using 20 micrograms ml-1 BLF and an incubation time of 150 min, elicited varying anticandidal activity against 35 isolates belonging to six different Candida species. Thus, BLF was fungicidal for the six Candida species in the following decreasing order, C. tropicalis > C. krusei > C. albicans > C. guilliermondii > C. parapsilosis > C. glabrata; the latter being the most resistant. These Candida species also demonstrated significant intra-species variation in susceptibility to the protein (P < 0.05). When the yeast cells exposed to BLF were examined by cryo-scanning electron microscopy, profound cell wall changes such as cell surface blebs, swelling and cell collapse were noted. These findings suggest that lactoferrin, a constituent of saliva, may differentially modulate the carriage of Candida species in the oral cavity.

Kodamaea nitidulidarum, Candida restingae and Kodamaea anthophila, three new related yeast species from ephemeral flowers

Three new yeast species were discovered during studies of yeasts associated with ephemeral flowers in Brazil, Australia and Hawaii. Their physiological and morphological similarity to Kodamaea (Pichia) ohmeri suggested a possible relationship to that species, which was confirmed by rDNA sequencing. Kodamaea nitidulidarum and Candida restingae were found in cactus flowers and associated nitidulid beetles in sand dune ecosystems (restinga) of South-eastern Brazil. Over 350 strains of Kodamaea anthophila were isolated from Hibiscus and morning glory flowers (Ipomoea spp.) in Australia, and from associated nitidulid beetles and Drosophila hibisci. A single isolate came from a beach morning glory in Hawaii. Expansion of the genus Kodamaea to three species modified the existing definition of the genus only slightly. The type and isotype strains are as follows: K. nitidulidarum strains UFMG96-272T (h+; CBS 8491T) and UFMG96-394I (h-; CBS 8492I); Candida restingae UFMG96-276T (CBS 8493T); K. anthophila strains UWO(PS)95-602.1T (h+; CBS 8494T), UWO(PS)91-893.2I (h-; CBS 8495I) and UWO(PS)95-725.1I (h-; CBS 8496I).

Adhesion of Helicobacter pylori to yeast cells

In order to get information as to whether direct interaction of H. pylori and yeasts may modulate the course of H. pylori infections, the adhesion of H. pylori to C. albicans, C. glabrata, C. guilliermondii, C. krusei, C. parapsilosis, C. tropicalis and S. cereviseae was investigated. H. pylori adhered significantly more frequently to C. tropicalis (adhesion ratio > 10%) than to the other yeasts (adhesion ratios < 5%). On an average, no significant difference to the adhesion ratios of E. coli and S. aureus was found. Electron microscopic examinations showed that H. pylori cells contacted the cells of C. tropicalis either by knob-like structures or by close surface-to-surface adhesion. Cholesterol-depleted H. pylori cells adhered to the yeast no more than cholesterol-carrying cells. There was no indication that a direct cooperation with yeasts plays a role in H. pylori infections.

Regulation of peroxisomal proteins and organelle proliferation by multiple carbon sources in the methylotrophic yeast, Candida boidinii

A methylotrophic yeast, Candida boidinii, was grown on various combinations of peroxisome-inducing carbon source(s) (PIC(s)), i.e. methanol, oleate and D-alanine, and the regulation of peroxisomal proteins (both matrix and membrane ones) and organelle proliferation were studied. This regulation was followed (1) at the protein or enzyme level by means of the peroxisomal enzyme activity and Western analysis; (2) at the mRNA level by Northern analysis; and (3) at the organelle level by direct observation of peroxisomes under a fluorescent microscope. Peroxisomal proliferation was followed in vivo by using a C. boidinii strain producing a green fluorescent protein having peroxisomal targeting signal 1. When multiple PICs were used for cell growth, C. boidinii induced specific peroxisomal proteins characteristic of all PIC(s) present in the medium, responding to all PIC(s) simultaneously. Thus, these PICs were considered to induce peroxisomal proliferation independently and not to repress peroxisomes induced by other PICs. Next, the sensitivity of the peroxisomal induction to glucose repression was studied. While the peroxisomal induction by methanol or oleate was completely repressed by glucose, the D-alanine-induced activities of D-amino acid oxidase and catalase, Pmp47, and the organelle proliferation were not. These results indicate that peroxisomal proliferation in yeasts is not necessarily sensitive to glucose repression. Lastly, this regulation was shown to occur at the mRNA level.

Evaluation of endpoints for antifungal susceptibility determinations with LY303366

We have previously reported poor correlation between the in vitro fungicidal activity of LY303366 and MIC results in RPMI medium based upon the manufacturer's suggested susceptibility endpoint, lack of visual growth. Additionally, we have noted a significant trailing effect with LY303366 when MICs are determined in RPMI medium. These observations have led us to evaluate an alternative susceptibility endpoint for LY303366, an 80% reduction in growth compared with control (similar to that utilized for azoles). Two isolates each of Candida albicans, Candida glabrata, and Candida tropicalis were selected for testing. MICs were determined for LY303366 in RPMI 1640 medium buffered with morpholinepropanesulfonic acid. MICs were determined with suggested (MIC100) and experimental (MIC80) endpoints. The minimal fungicidal concentration (MFC) of LY303366 for each isolate was also determined. Time-kill curves were determined in RPMI medium with each isolate at concentrations of LY303366 ranging from 0.125 to 16x MIC80 to assess the correlation between MIC80 and fungicidal activity. Lastly, fungi exposed to LY303366 were examined via scanning electron microscope (SEM) for evidence of drug-induced ultrastructure change. MIC80s for test isolates ranged from 0.015 to 0.12 microgram/ml and were consistently three to five wells less than MIC100s. Good correlation was observed between fungicidal activity, as assessed by kill curves, and the MIC80. SEM data revealed significant ultrastructure changes induced by LY303366 even at sub-MIC80s. Based on our results demonstrating better correlation between MIC80 and fungicidal activity, i.e., time-kill curves and MFCs, we suggest that 80% reduction in visible growth be utilized as the endpoint for susceptibility determinations with LY303366 in RPMI medium.

Quantification of thigmotropism (contact sensing) of Candida albicans and Candida tropicalis

To quantify the thigmotropism, we adapted the our previous method using a chemotaxifilter system in combination with a bioluminescent adenosine triphosphate (ATP) assay based on firefly luciferase-luciferin system and analyzed the relationship between the ability of germ tube formation and thigmotropism of C. albicans and C. tropicalis. Both the ability to form germ tube and the amount of hyphae exhibiting thigmotropism varied depending upon both the species and strains of Candida. C. albicans formed more germ tubes than C. tropicalis. A good correlation was observed between the ability to form a germ tube and the capacity for thigmotropism, and the results gave a level of significance (p < 0.05). Further, SEM observation revealed that relatively long hyphae of C. tropicalis with penetrated through the pores of filter membrane. This phenomenon may be of importance in the development of pathogenesis of C. tropicalis as well as C. albicans.

Voriconazole (UK-109,496) inhibits the growth and alters the morphology of fluconazole-susceptible and -resistant Candida species

The effects of voriconazole on the growth, ultrastructure, and leakage of cytoplasmic materials of Candida species were investigated. MIC data showed that voriconazole was more active than fluconazole. Exposure of yeast to voriconazole caused growth inhibition, cell wall thinning, and cell membrane degradation. Neither cell collapse nor release of cytoplasmic materials was observed in the treated cells.

Changes in the starvation response through covalent cell attachment

Covalent attachment of Candida utilis cells, possibly simulating natural microbial immobilizations, stimulated stable and significant enhancement of extracellular production of alkaline protease, specifically induced by four different starvation conditions. The enzyme analysis confirmed the identity of the proteases released under all conditions of starvation and no parallel production of other proteolytic enzyme. The enhancement phenomenon as a uniform and stable effect of the whole cell immobilization is discussed in relation to the effect of multipoint, cell-solid surface contact, potentially bringing positive modulations of complex, cellular functions.

Candida novakii, sp. nov. a new anamorphic yeast species of ascomycetous affinity

Two strains of an undescribed species of the genus Candida were isolated from decaying wood of Quercus sp. A description of the new species Candida novakii is given.

Candida and Torulopsis: a blinded evaluation of use of pseudohypha formation as basis for identification of medically important yeasts

Seventy yeast isolates representing species in the genera Candida and Torulopsis but excluding Candida albicans were examined in three laboratories for production of pseudohyphae in Dalmau cultures. The microscopic morphology of the isolates was scrutinized by four individuals experienced in yeast identification and three inexperienced persons, all of whom were blinded as to the putative identification of the yeasts. For 49 (70%) of the 70 isolates, the seven observers recorded comparable scores for morphology, but 5 (7%) of the isolates showed extreme variation in recorded morphologies, from true hyphae formed to no pseudohyphae formed. Isolates of Candida parapsilosis and Torulopsis glabrata consistently did and did not form pseudohyphae, respectively: however, other Candida and Torulopsis spp. did not always express their expected morphologies. In 48 (19%) of 252 readings (seven observers), 36 isolates of Candida spp. were scored as forming no pseudohyphae, and in 22 (9.2%) of 238 readings, 34 isolates of Torulopsis spp. were recorded as forming true hyphae or pseudohyphae. These results show that pseudohypha formation is not a reliable characteristic for identification of yeasts at the genus level; we suggest that the merger of Torulopsis spp. into the genus Candida should be finally accepted.

A specialized nucleosome modulates transcription factor access to a C. glabrata metal responsive promoter

The ability of DNA binding transcription factors to access cis-acting promoter elements is critical for transcriptional responses. We demonstrate that rapid transcriptional autoactivation by the Amt1 Cu metalloregulatory transcription factor from the opportunistic pathogenic yeast Candida glabrata is dependent on rapid metal-induced DNA binding to a single metal response element (MRE). In vivo footprinting and chromatin-mapping experiments demonstrate that the MRE and a homopolymeric (dA x dT) element adjacent to the MRE are packaged into a positioned nucleosome that exhibits homopolymeric (dA x dT)-dependent localized distortion. This distortion is critical for rapid Amt1 binding to the MRE, for Cu-dependent AMT1 gene transcription, and for C. glabrata cells to mount a rapid transcriptional response to Cu for normal metal detoxification. The AMT1 promoter represents a novel class of specialized nucleosomal structures that links rapid transcriptional responses to the biology of metal homeostasis.

Evidence for a beta 1 integrin fibronectin receptor in Candida tropicalis

The binding of Candida tropicalis to fibronectin (FN) was studied in order to characterize the FN receptor in this species. FN binding was saturable at a concentration of 1.8 x 10(-9) M and exhibited a Kd of 2.3 x 10(-9) M and a receptor density of 854 receptors per cell. Extracts of C. tropicalis cell membrane at dilutions of 1:100-1:1000 significantly inhibited the binding of 3H-labeled FN to C. tropicalis cells (P < .03). Purified FN, antibodies to the integrin alpha 5 beta 1 (FN receptor on human placenta), and antibodies specific for the integrin beta 1 subunit recognized a C. tropicalis membrane protein of 125 +/- 25 kDa on immunoblots. Immunoprecipitation of radiolabeled proteins from C. tropicalis with purified human FN yielded a protein of 105 +/- 15 kDa. Thus, C. tropicalis expresses a protein with antigenic and functional similarity to the vertebrate beta 1 integrin FN receptor.

Immunoelectron microscopic observation of the behaviors of peroxisomal enzymes inducibly synthesized in an n-alkane-utilizable yeast cell, Candida tropicalis

We reported that immunoelectron microscopy was an excellent tool for determining the subcellular localization of thiolase isozymes, acetoacetyl-CoA thiolase (T-I) and 3-ketoacyl-CoA thiolase (T-III) in n-alkane-grown Candida tropicalis cells (KAMASAWA, N. et al., (1992). Cell Struct. Funct., 17: 203-207). Current investigation on the visualization of other peroxisomal enzymes, acyl-CoA oxidase (ACO), catalase (KAT), carnitine acetyltransferase (CAT), isocitrate lyase (ICL) and malate synthase (MS), showed that ACO localized in peroxisomes, KAT in peroxisomes and cytoplasm, and CAT in peroxisomes, mitochondria and cytoplasm. Most of ICL and MS were found in peroxisomes. These results agreed with previous biochemical studies and supported the presumed roles of these enzymes. The same technique was applied to study the process of synthesis and localization of these enzymes early in the cultivation period in n-alkane medium when peroxisomes began to proliferate. ACO and T-III were rapidly induced after transfer of cells from glucose- to n-alkane-media. There was a drastic change of their location from cytoplasm to peroxisomes between 1 h and 2 h after the transfer, while T-I, KAT and CAT were moderately induced in cytoplasm and their location was gradually changed to each organelle. ICL and MS, the key enzymes in the glyoxylate cycle, were already localized in peroxisomes in the glucose-grown cells and respective inducible enzymes also were gradually localized there. This visual analysis is useful for the vivid elucidation of the process of peroxisome proliferation and enzyme transport within a cell.

Candida'the cancer of silastic'

Candida species have the propensity to colonize and erode into the surface of silastic causing a loss of function. Colonization of silastic tracheo-oesophageal speaking-valves is an important cause of valve failure post-laryngectomy: the exact nature of the colonization is unknown and light microscopic studies have not been reported previously. Microbiological examination of scrapings taken from the colonized oesophageal surface of failed speaking valves was arranged before sectioning for light microscopy. Conventional ultrathin sectioning of silastic was difficult, therefore 15 micrometre sections were cut after cooling the material to -30 degrees C. These sections were then stained with toluidine blue; Candida species taking up the stain. Microbiological examination of the colonies confirmed the predominance of Candida species in the biofilm. Light microscopy of the 15 micrometer sections revealed that the Candida colonies had invaded the silastic. This work demonstrates that the colonization of the silastic valve prosthesis in the oesophageal area is due predominantly to Candida species which actively invade the structure of the silastic. This is an important cause of speaking-valve failure post-laryngectomy.

Modification of the targeting presequence of the bovine cytochrome P-450scc precursor lifting tissue-specific restrictions on its mitochondrial import

It has been found that a recombinant cytochrome P-450scc precursor supplemented with an extra MRGSH6GIR sequence at the NH2-terminus (6His-pP450scc) is imported into isolated rat liver and heart mitochondria as well as into yeast mitochondria. The import is coupled with proteolytic processing of the precursor resulting in the mature size form of cytochrome P-450scc. Modification of the targeting presequence responsible for its increased positive charge is supposed to lift the previously suggested tissue-specific restrictions on the pP450scc import into mitochondria.

The Candida boidinii peroxisomal membrane protein Pmp30 has a role in peroxisomal proliferation and is functionally homologous to Pmp27 from Saccharomyces cerevisiae

The mechanism of peroxisome proliferation is poorly understood. Candida boidinii is a methylotrophic yeast that undergoes rapid and massive peroxisome proliferation and serves as a good model system for this process. Pmp30A and Pmp30B (formerly designated Pmp31 and Pmp32, respectively) are two closely related proteins in a polyploid strain of this yeast that are strongly induced by diverse peroxisome proliferators such as methanol, oleate, and D-alanine. The function of these proteins is not understood. To study this issue, we used a recently described haploid strain (S2) of C. boidinii that can be manipulated genetically. We now report that strain S2 contains a single PMP30 gene very similar in sequence (greater than 93% identity at the DNA level) to PMP30A and PMP30B. When PMP30 was disrupted, cell growth on methanol was greatly inhibited, and cells grown in both methanol and oleate had fewer, larger, and more spherical peroxisomes than wild-type cells. A similar phenotype was recently described for Saccharomyces cerevisiae cultured on oleate in which PMP27, which encodes a protein of related sequence that is important for peroxisome proliferation, was disrupted. To determine whether Pmp27 is a functional homolog of Pmp30, gentle complementation was performed. PMP30A was expressed in the PMP27 disruptant of S. cerevisiae, and PMP27 was expressed in the PMP30 disruptant of C. boidinii S2. Complementation, in terms of both cell growth and organelle size, shape, and number, was successful in both directions, although reversion to a wild-type phenotype was only partial for the PMP30 disruptant. We conclude that these proteins are functional homologs and that both Pmp30 and Pmp27 have a direct role in proliferation and organelle size rather than a role in a specific peroxisomal metabolic pathway of substrate utilization.

Fluconazole resistance due to energy-dependent drug efflux in Candida glabrata

We report on the mechanism of fluconazole resistance in Candida glabrata from a case of infection in which pre- and posttreatment isolates were available for comparison. The resistant, posttreatment isolate was cross-resistant to ketoconazole and itraconazole, in common with other azole-resistant yeasts. Resistance was due to reduced levels of accumulation of [3H]fluconazole rather than to changes at the level of ergosterol biosynthesis. Studies with metabolic or respiratory inhibitors showed that this phenomenon was a consequence of energy-dependent drug efflux, as opposed to a barrier to influx. Since energy-dependent efflux is a characteristic of multidrug resistance in bacteria, yeasts, and mammalian cells, we investigated the possibility that fluconazole resistance is mediated by a multidrug resistance-type mechanism. Benomyl, a substrate for the Candida albicans multidrug resistance protein, showed competition with fluconazole for efflux from resistance C. glabrata isolates, consistent with a common efflux mechanism for these compounds. By contrast, other standard substrates or inhibitors of multidrug resistance proteins had no effect on fluconazole efflux. In conclusion, we have identified energy-dependent efflux of fluconazole, possibly via a multidrug resistance-type transporter, as the mechanism of resistance to fluconazole in C. glabrata.

Pseudomembranous oral candidiasis in HIV infection: ultrastructural findings

A light and electron microscopic investigation of pseudomembranous candidiasis in HIV infection was undertaken as there is little data available on the ultrastructural features of the invasive phase of Candida in this disease. On examination of biopsy specimens of four patients, histopathology revealed the classic features of superficial candidiasis, including hyphal penetration down to the spinous cell layer, parakeratosis, acanthosis and spongiosis of the infected, superficial epithelium. However, in one case, hyphae traversed the entire epithelium and crossed the basal membrane, invading the adjacent connective tissue. Ultrastructural investigations revealed initial hyphal penetration through the intercellular spaces, possibly demonstrating thigmotropism. However, hyphal penetration was not solely confined to intercellular spaces, as some specimens demonstrated hyphal elements traversing both the cytoplasm and the nuclei of the spinous cells. In these areas of the epithelium appressoria-like appendages were often found at the hyphal tip. These phenomena, commonly described in plant fungi, have rarely been described in human material. Pools of desmosomes were seen in the vicinity of the hyphal pathways, implying that the penetration procedure is associated with detachment and congregation of desmosomes, possibly by enzymatic means. Interestingly, the host immune response to fungal invasion appeared to be minimal, as no immune-effector cells were seen closely associated with either the blastospores or the hyphae in any of the tissues examined. Whether the foregoing events are exaggerated by the abortive immune response seen in HIV-infected patients, or common in immunocompetent individuals during candidal invasion of epithelia, needs to be ascertained by further studies.

Limitations in tandem scanning confocal microscopy as a diagnostic tool for microbial keratitis

One potential application of tandem scanning confocal microscopy is the detection of in vivo pathogens. Our study of an experimental model of Acanthamoeba keratitis demonstrates that while this technology can successfully detect certain organisms, there are currently limitations. These limitations relate to instrument configuration, movement of either the tissue or the microscope, difficulty in reproducibly returning to the area of interest for serial examination, the lack of a distinctive morphology of some pathogens, and limited resolution of the microscope.

Frequency of Candida sp infection in tuberculous patients with acquired immunodeficiency syndrome: morphological and immunocytochemical study in sputum

Sputum samples from AIDS patients with and without pulmonary tuberculosis were analyzed morphologically and immunocytochemically to determine the frequency of occurrence of Candida sp. Mycobacterial infection was detected by bacterioscopy and/or culture and cytological evaluation was performed using Papanicolaou and Toluidine Blue staining. Immunoreaction for Candida sp was performed using polyclonal antibody in selected cases with fungal structures in smears stained by the Papanicolaou or Toluidine Blue method. An increased frequency of Candida sp (2.5 times) was observed in the tuberculous group compared to the group of AIDS patients without tuberculosis. The Toluidine Blue stain showed good results for the detection of Candida sp in sputum. Due to the increased risk of this opportunistic infection among more severely immunocompromised patients. Toluidine Blue staining of sputum samples submitted to analysis seems to be a reliable screening method.

Predominant localization of non-specific lipid-transfer protein of the yeast Candida tropicalis in the matrix of peroxisomes

PXP-18 is a 14-kDa major peroxisomal protein of the yeast Candida tropicalis and a homologue of the non-specific lipid-transfer protein (nsLTP) of mammals. Mammalian nsLTP is thought to facilitate the contact of membranes, to stimulate lipid-transfer between them. If PXP-18 functions like nsLTP, it must be present on organelle membranes. Immunoelectron microscopy of C. tropicalis cells indicated that gold particles, which visualized PXP-18, localized exclusively in the matrix of peroxisomes. Subcellular fractionation followed by Western blotting revealed the association of PXP-18 with peroxisomes in C. tropicalis cells. An enzyme-linked immunosorbent assay revealed that almost all the PXP-18 associated with peroxisomes was detectable after the solubilization of the organelle but not before, implying the predominance of PXP-18 inside peroxisomes. This differential assay was applied to the intracellular import of the intact and truncated PXP-18s expressed in Saccharomyces cerevisiae cells. Most of the intact PXP-18 was shown to be imported into the matrix of host-cell peroxisomes, whereas the truncated PXP-18, which lacked the C-terminal tripeptide Pro-Lys-Leu, no longer targeted peroxisomes. These results are consistent with the view that PXP-18 is the matrix protein of peroxisomes and must function in a system other than that of lipid transfer.

Synergism between the antifungal agents amphotericin B and alkyl glycerol ethers

The alkyl glycerol ether rac-1-O-dodecylglycerol inhibited the growth of members of two genera of yeasts, Candida and Cryptococcus, and was strongly synergistic with amphotericin B. At one-half its MIC, dodecylglycerol decreased the MIC of amphotericin B by as much as 80-fold. This high degree of synergism between dodecylglycerol and amphotericin B was demonstrated against a number of species of yeasts including Candida albicans, Candida tropicalis, Candida parapsilosis, Cryptococcus neoformans, Cryptococcus albidus, and Cryptococcus laurentii. All fractional inhibitory concentrations (for all strains and species) were calculated to be less than 1, and most were less than 0.6, again demonstrating strong synergism. Other alkyl glycerol ethers with alkyl chain lengths ranging from 8 to 18 carbon atoms were also found to be synergistic with amphotericin B against C. neoformans and C. albicans. Electron microscopy experiments showed that C. neoformans grown in the presence of dodecylglycerol had severely abnormal, deformed capsules. Although the mechanism of action of dodecylglycerol is not known, dodecylglycerol was not simply acting as a detergent. The natural detergent sodium deoxycholate could not substitute for dodecylglycerol. At comparable and higher concentrations, sodium deoxycholate had no fungicidal effect on its own, nor did it potentiate the activity of amphotericin B. Dodecylglycerol did not interact synergistically with the water-soluble antifungal agent fluconazole. The lipid-soluble hydrophobic properties of amphotericin B appear to be important for this synergistic effect, in that alkyl glycerol ethers could promote synergism with amphotericin B by potentially increasing the interaction between membrane-bound ergosterol and amphotericin B.