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.

Evolution of pathogenicity and sexual reproduction in eight Candida genomes

Candida species are the most common cause of opportunistic fungal infection worldwide. Here we report the genome sequences of six Candida species and compare these and related pathogens and non-pathogens. There are significant expansions of cell wall, secreted and transporter gene families in pathogenic species, suggesting adaptations associated with virulence. Large genomic tracts are homozygous in three diploid species, possibly resulting from recent recombination events. Surprisingly, key components of the mating and meiosis pathways are missing from several species. These include major differences at the mating-type loci (MTL); Lodderomyces elongisporus lacks MTL, and components of the a1/2 cell identity determinant were lost in other species, raising questions about how mating and cell types are controlled. Analysis of the CUG leucine-to-serine genetic-code change reveals that 99% of ancestral CUG codons were erased and new ones arose elsewhere. Lastly, we revise the Candida albicans gene catalogue, identifying many new genes.

Candida parapsilosis, an emerging fungal pathogen

SUMMARY

Candida parapsilosis is an emerging major human pathogen that has dramatically increased in significance and prevalence over the past 2 decades, such that C. parapsilosis is now one of the leading causes of invasive candidal disease. Individuals at the highest risk for severe infection include neonates and patients in intensive care units. C. parapsilosis infections are especially associated with hyperalimentation solutions, prosthetic devices, and indwelling catheters, as well as the nosocomial spread of disease through the hands of health care workers. Factors involved in disease pathogenesis include the secretion of hydrolytic enzymes, adhesion to prosthetics, and biofilm formation. New molecular genetic tools are providing additional and much-needed information regarding C. parapsilosis virulence. The emerging information will provide a deeper understanding of C. parapsilosis pathogenesis and facilitate the development of new therapeutic approaches for treating C. parapsilosis infections.

Candida dubliniensis sp. nov.: phenotypic and molecular characterization of a novel species associated with oral candidosis in HIV-infected individuals

Atypical oral Candida isolates were recovered from 60 HIV-infected and three HIV-negative individuals. These organisms were germ-tube-positive and produced abundant chlamydospores which were frequently arranged in triplets or in contiguous pairs. They belonged to C. albicans serotype A and had atypical carbohydrate assimilation profiles. Fingerprinting the genomic DNA of a selection of these organisms with the C. albicans-specific probe 27A and five separate oligonucleotides, homologous to eukaryotic microsatellite repeat sequences, demonstrated that they had a very distinct genomic organization compared to C. albicans and C. stellatoidea. This was further established by random amplified polymorphic DNA (RAPD) and karyotype analysis. Comparison of 500 bp of the V3 variable region of the large ribosomal subunit genes from nine atypical isolates and the corresponding sequences determined from C. albicans, C. stellatoidea, C. tropicalis, C. parapsilosis, C. glabrata, C. kefyr and C. krusei showed that they atypical organisms formed a homogeneous cluster (100% similarity) that was significantly different from the other Candida species analysed, but was most closely related to C. albicans and C. stellatoidea. These genetic data combined with the phenotypic characteristics of these atypical organisms strongly suggest that they constitute a novel species within the genus Candida for which the name Candida dubliniensis is proposed.

Candida biofilms on implanted biomaterials: a clinically significant problem

In recent years there has been an increasing appreciation that microbial biofilms are ubiquitous, which has resulted in a number of studies on infectious diseases from a biofilm perspective. Biofilms are defined as structured microbial communities that are attached to a surface and encased in a matrix of exopolymeric material. A wide range of biomaterials used in clinical practice have been shown to support colonization and biofilm formation by Candida spp., and the increase in Candida infections in the last decades has almost paralleled the increase and widespread use of a broad range of medical implant devices, mainly in populations with impaired host defenses. Formation of Candida biofilms has important clinical repercussions because of their increased resistance to antifungal therapy and the ability of cells within biofilms to withstand host immune defenses. Further recognition and understanding of the role of Candida biofilms in human infection should help in the clinical management of these recalcitrant infections.

Comparison of biofilms formed by Candida albicans and Candida parapsilosis on bioprosthetic surfaces

Little is known about fungal biofilms, which may cause infection and antibiotic resistance. In this study, biofilm formation by different Candida species, particularly Candida albicans and C. parapsilosis, was evaluated by using a clinically relevant model of Candida biofilm on medical devices. Candida biofilms were allowed to form on silicone elastomer and were quantified by tetrazolium (XTT) and dry weight (DW) assays. Formed biofilm was visualized by using fluorescence microscopy and confocal scanning laser microscopy with Calcofluor White (Sigma Chemical Co., St. Louis, Mo.), concanavalin A-Alexafluor 488 (Molecular Probes, Eugene, Oreg.), and FUN-1 (Molecular Probes) dyes. Although minimal variations in biofilm production among invasive C. albicans isolates were seen, significant differences between invasive and noninvasive isolates (P < 0.001) were noted. C. albicans isolates produced more biofilm than C. parapsilosis, C. glabrata, and C. tropicalis isolates, as determined by DW assays (P was <0.001 for all comparisons) and microscopy. Interestingly, noninvasive isolates demonstrated a higher level of XTT activity than invasive isolates. On microscopy, C. albicans biofilms had a morphology different from that of other species, consisting of a basal blastospore layer with a dense overlying matrix composed of exopolysaccharides and hyphae. In contrast, C. parapsilosis biofilms had less volume than C. albicans biofilms and were comprised exclusively of clumped blastospores. Unlike planktonically grown cells, Candida biofilms rapidly (within 6 h) developed fluconazole resistance (MIC, >128 microg/ml). Importantly, XTT and FUN-1 activity showed biofilm cells to be metabolically active. In conclusion, our data show that C. albicans produces quantitatively larger and qualitatively more complex biofilms than other species, in particular, C. parapsilosis.

An adhesin of the yeast pathogen Candida glabrata mediating adherence to human epithelial cells

Candida glabrata is an important fungal pathogen of humans that is responsible for about 15 percent of mucosal and systemic candidiasis. Candida glabrata adhered avidly to human epithelial cells in culture. By means of a genetic approach and a strategy allowing parallel screening of mutants, it was possible to clone a lectin from a Candida species. Deletion of this adhesin reduced adherence of C. glabrata to human epithelial cells by 95 percent. The adhesin, encoded by the EPA1 gene, is likely a glucan-cross-linked cell-wall protein and binds to host-cell carbohydrate, specifically recognizing asialo-lactosyl-containing carbohydrates.

Gut origin of sepsis: a prospective study investigating associations between bacterial translocation, gastric microflora, and septic morbidity

AIMS

To investigate the "gut origin of sepsis" hypothesis.

METHODS

Prospective controlled study of 279 surgical patients in which cultures of nasogastric aspirates were compared with those obtained from mesenteric lymph nodes taken at laparotomy and the organisms cultured from subsequent septic complications. Bacterial translocation was confirmed if positive cultures were obtained from mesenteric lymph nodes. Postoperative sepsis was defined as any positive culture in the postoperative period. Bacterial species obtained in gastric microflora, mesenteric lymph nodes, and postoperative septic complications were compared.

RESULTS

Only 85/279 patients (31%) had a sterile nasogastric aspirate; the most frequently identified organism was Candida spp. (54%) and the most common enteric organism cultured was E coli (20%). Multiple organisms were isolated in 39% and occurred more frequently in patients aged over 70 years, those undergoing non-elective surgery, and in those requiring proximal gastrointestinal surgery. Postoperative sepsis was more common in these patients. Bacterial translocation occurred in 21% and was significantly more frequent in those with multiple organisms in their nasogastric aspirates. E coli was the commonest organism isolated from the lymph node specimens (48%) and septic foci (53%). Fungal translocation did not occur. An identical genus was identified in the nasogastric aspirate and the septic focus in 30% of patients, in the nasogastric aspirate and the lymph node in 31%, and in the lymph node and a postoperative septic focus in 45%.

CONCLUSIONS

Proximal gut colonisation is associated with both increased bacterial translocation and septic morbidity. The commonality of organisms identified supports the gut origin of sepsis hypothesis.

Antifungal susceptibility testing: practical aspects and current challenges

Development of standardized antifungal susceptibility testing methods has been the focus of intensive research for the last 15 years. Reference methods for yeasts (NCCLS M27-A) and molds (M38-P) are now available. The development of these methods provides researchers not only with standardized methods for testing but also with an understanding of the variables that affect interlaboratory reproducibility. With this knowledge, we have now moved into the phase of (i) demonstrating the clinical value (or lack thereof) of standardized methods, (ii) developing modifications to these reference methods that address specific problems, and (iii) developing reliable commercial test kits. Clinically relevant testing is now available for selected fungi and drugs: Candida spp. against fluconazole, itraconazole, flucytosine, and (perhaps) amphotericin B; Cryptococcus neoformans against (perhaps) fluconazole and amphotericin B; and Aspergillus spp. against (perhaps) itraconazole. Expanding the range of useful testing procedures is the current focus of research in this area.

Adhesion in Candida spp

Microbial adherence is one of the most important determinants of pathogenesis, yet very few adhesins have been identified from fungal pathogens. Four structurally related adhesins, Hwp1, Ala1p/Als5p, Als1p, from Candida albicans and Epa1p from Candida glabrata, are members of a class of proteins termed glycosylphosphatidylinositol-dependent cell wall proteins (GPI-CWP). These proteins have N-terminal signal peptides and C-terminal features that mediate glycosylphosphatidylinositol (GPI) membrane anchor addition, as well as other determinants leading to attachment to cell wall glucan. While common signalP/GPI motifs facilitate cell surface expression, unique features mediate ligand binding specificities of adhesins. The first glimpse of structural features of putative adhesins has come from biophysical characterizations of the N-terminal domain of Als5p. One protein not in the GPI-CWP class that was initially described as an adhesin, Int1p, has recently been shown to be similar to Bud4p of Saccharomyces cerevisiae in primary amino acid sequence, in co-localizing with septins and in functioning in bud site selection. Progress in understanding the role of adhesins in oroesophageal candidiasis has been made for Hwp1 in a study using beige athymic and transgenic epsilon 26 mice that have combined defects in innate and acquired immune responses. Searches of the C. albicans genome for proteins in the GPI-CWP class has led to the identification of a subset of genes that will be the focus of future efforts to identify new Candida adhesins.

Heavy metal removal from sediments by biosurfactants

Batch washing experiments were used to evaluate the feasibility of using biosurfactants for the removal of heavy metals from sediments. Surfactin from Bacillus subtilis, rhamnolipids from Pseudomonas aeruginosa and sophorolipid from Torulopsis bombicola were evaluated using a metal-contaminated sediment (110mg/kg copper and 3300mg/kg zinc). A single washing with 0.5% rhamnolipid removed 65% of the copper and 18% of the zinc, whereas 4% sophorolipid removed 25% of the copper and 60% of the zinc. Surfactin was less effective, removing 15% of the copper and 6% of the zinc. The technique of ultrafiltration and zeta potential measurements were used to determine the mechanism of metal removal by the surfactants. It was then postulated that metal removal by the biosurfactants occurs through sorption of the surfactant on to the soil surface and complexation with the metal, detachment of the metal from the soil into the soil solution and hence association with surfactant micelles. Sequential extraction procedures were used on the sediment to determine the speciation of the heavy metals before and after surfactant washing. The carbonate and oxide fractions accounted for over 90% of the zinc present in the sediments. The organic fraction constituted over 70% of the copper. Sequential extraction of the sediments after washing with the various surfactants indicated that the biosurfactants, rhamnolipid and surfactin could remove the organically-bound copper and that the sophorolipid could remove the carbonate and oxide-bound zinc. Therefore, heavy metal removal from sediments is feasible and further research will be conducted.

Oral supplementation with Lactobacillus casei subspecies rhamnosus prevents enteric colonization by Candida species in preterm neonates: a randomized study

BACKGROUND

Colonization by Candida species is the most important predictor of the development of invasive fungal disease in preterm neonates, and the enteric reservoir is a major site of colonization. We evaluated the effectiveness of an orally supplemented probiotic (Lactobacillus casei subspecies rhamnosus; Dicoflor [Dicofarm spa]; 6 x 10(9) cfu/day) in the prevention of gastrointestinal colonization by Candida species in preterm, very low birth weight (i.e., < 1500-g) neonates during their stay in a neonatal intensive care unit.

METHODS

Over a 12-month period, a prospective, randomized, blind, clinical trial that involved 80 preterm neonates with a very low birth weight was conducted in a large tertiary neonatal intensive care unit. During the first 3 days of life, the neonates were randomly assigned to receive either an oral probiotic added to human (maternal or pooled donors') milk (group A) or human milk alone (group B) for 6 weeks or until discharge from the NICU, if the neonate was discharged before 6 weeks. On a weekly basis, specimens obtained from various sites (i.e., oropharyngeal, stool, gastric aspirate, and rectal specimens) were collected from all patients for surveillance culture, to assess the occurrence and intensity of fungal colonization in the gastrointestinal tract.

RESULTS

The incidence of fungal enteric colonization (with colonization defined as at least 1 positive culture result for specimens obtained from at least 1 site) was significantly lower in group A than in group B (23.1% vs. 48.8%; relative risk, 0.315 [95% confidence interval, 0.120-0.826]; P = .01). The numbers of fungal isolates obtained from each neonate (P = .005) and from each colonized patient (P = .005) were also lower in group A than in group B. L. casei subspecies rhamnosus was more effective in the subgroup of neonates with a birth weight of 1001-1500 g. There were no changes in the relative proportions of the different Candida strains. No adverse effects potentially associated with the probiotic were recorded.

CONCLUSIONS

Orally administered L. casei subspecies rhamnosus significantly reduces the incidence and the intensity of enteric colonization by Candida species among very low birth weight neonates.

Adherence of Candida albicans and other Candida species to mucosal epithelial cells

To study the possible involvement of candidal adherence in mucosal colonization, we examined the in vitro adherence capabilities of seven Candida species. Adherence was evaluated by direct microscopic examination and by a quantitative radiometric adherence test. The results indicate that C. albicans adheres to vaginal and buccal epithelial cells to a significantly greater degree (P less than 0.01) than the other species tested. C. tropicalis and C. stellatoidea demonstrated moderate adherence capabilities, while C. parapsilosis adhered only to a slight degree. Other species failed to interact with isolated mucosal cells. These findings suggest that there is a relationship between the adherence capabilities of the Candida species and their abilities to colonize mucosal surfaces, since those species which adhere are those which most frequently colonize mucosal surfaces. C. albicans was found to be adherent under a variety of environmental conditions. Stationary-phase blastospores of C. albicans were found to be more adherent than logarithmic-phase yeasts, and larger blastospore cell-to-epithelial cell ratios resulted in greater adherence values. The actual number of adherent yeasts varied considerably when epithelial cells were obtained from different donors.

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.

Hydrophobic interaction in Candida albicans and Candida tropicalis adherence to various denture base resin materials

The effects of hydrophobicities of substrate surfaces on microbial adherence were examined by using Candida albicans and Candida tropicalis and 21 denture base resin materials. With increasing surface free energy of resin plates, increasing adherence of C. albicans and decreasing adherence of C. tropicalis were observed. The surface free energy of C. albicans is higher than that of all resin material surfaces, and C. tropicalis has surface free energy lower than that of all materials used. In calculation of the changes of free energy accompanying the adherence, the higher adherence tendency was accompanied by a lower value for the free energy change in both species. From a different standpoint, the closer the surface free energy of the substrate surface and the microorganism, the higher was the probability of adherence.

Biocontrol ability and action mechanism of food-isolated yeast strains against Botrytis cinerea causing post-harvest bunch rot of table grape

Strains belonging to the species Saccharomyces cerevisiae, Wickerhamomyces anomalus, Metschnikowia pulcherrima and Aureobasidium pullulans, isolated from different food sources, were tested in vitro as biocontrol agents (BCAs) against the post-harvest pathogenic mold Botrytis cinerea. All yeast strains demonstrated antifungal activity at different levels depending on species and medium. Killer strains of W. anomalus and S. cerevisiae showed the highest biocontrol in vitro activity, as demonstrated by largest inhibition halos. The competition for iron and the ability to form biofilm and to colonize fruit wounds were hypothesized as the main action mechanisms for M. pulcherrima. The production of hydrolytic enzymes and the ability to colonize the wounds were the most important mechanisms for biocontrol activity in A. pullulans and W. anomalus, which also showed high ability to form biofilm. The production of volatile organic compounds (VOCs) with in vitro and in vivo inhibitory effect on pathogen growth was observed for the species W. anomalus, S. cerevisiae and M. pulcherrima. Our study clearly indicates that multiple modes of action may explain as M. pulcherrima provide excellent control of postharvest botrytis bunch rot of grape.

Current treatment strategies for disseminated candidiasis

The incidence of disseminated candidiasis has increased dramatically over the past several decades. Fortunately, in recent years, a variety of new antifungal agents have become available to treat these infections. On the basis of efficacy, safety, and cost considerations, fluconazole is the agent of choice for the empirical treatment of disseminated candidiasis in nonneutropenic, hemodynamically stable patients, unless a patient is suspected to be infected with an azole-resistant species (i.e., Candida glabrata or Candida krusei). For hemodynamically unstable or neutropenic patients, agents with broader species coverage, such as polyenes, echinocandins, or, possibly, voriconazole, are preferred for empirical treatment of candidemia. Modification of the initial, empirical regimen depends on the response to therapy and the subsequent identification of the species of the offending pathogen. Echinocandins or high-dose polyenes are preferred for the treatment of infections with C. glabrata or C. krusei. Central venous catheters should be removed from all patients who have disseminated candidiasis, if feasible, and antifungal therapy should be administered to all patients who have candidemia or proven candidiasis.

Isolation of Vaginal Lactobacilli and Characterization of Anti-Candida Activity

Healthy vaginal microbiota is dominated by Lactobacillus spp., which form a critical line of defence against pathogens, including Candida spp. The present study aims to identify vaginal lactobacilli exerting in vitro activity against Candida spp. and to characterize their antifungal mechanisms of action. Lactobacillus strains were isolated from vaginal swabs of healthy premenopausal women. The isolates were taxonomically identified to species level (L. crispatus B1-BC8, L. gasseri BC9-BC14 and L. vaginalis BC15-BC17) by sequencing the 16S rRNA genes. All strains produced hydrogen peroxide and lactate. Fungistatic and fungicidal activities against C. albicans, C. glabrata, C. krusei, C. tropicalis, C. parapsilosis and C. lusitaniae were evaluated by broth micro-dilution method. The broadest spectrum of activity was observed for L. crispatus BC1, BC4, BC5 and L. vaginalis BC15, demonstrating fungicidal activity against all isolates of C. albicans and C. lusitaniae. Metabolic profiles of lactobacilli supernatants were studied by 1H-NMR analysis. Metabolome was found to be correlated with both taxonomy and activity score. Exclusion, competition and displacement experiments were carried out to investigate the interference exerted by lactobacilli toward the yeast adhesion to HeLa cells. Most Lactobacillus strains significantly reduced C. albicans adhesion through all mechanisms. In particular, L. crispatus BC2, L. gasseri BC10 and L. gasseri BC11 appeared to be the most active strains in reducing pathogen adhesion, as their effects were mediated by both cells and supernatants. Inhibition of histone deacetylases was hypothesised to support the antifungal activity of vaginal lactobacilli. Our results are prerequisites for the development of new therapeutic agents based on probiotics for prophylaxis and adjuvant therapy of Candida infection.

Resistance of yeasts to azole-derivative antifungals

There are relatively few antifungal agents available for the treatment of systemic mycoses. The incidence of these infections, particularly among the immunocompromised, has increased significantly in recent years. Amphotericin B, flucytosine and the azole-derivatives--fluconazole, itraconazole and ketoconazole--are the only drugs of value in the treatment of systemic yeast infections currently available. To date resistance among individual yeast species or strains has only been a serious problem with flucytosine. However, resistance among Candida spp. to orally administered azole-derivatives has been observed. The frequency with which resistance has been described in clinical practice among yeasts differs considerably between the three azole antifungal agents. Fluconazole has been implicated in emergent resistance more frequently than ketoconazole, and ketoconazole more often than itraconazole. It must be a matter for concern that, by analogy with the known emergence of antibiotic-resistance among bacteria, that the widespread use of a drug inactive against a particular species may lead to an increased incidence of such infections. An international epidemiological survey is required to establish the extent and degree of resistance to the azole antifungals.

Transcriptome Assembly and Profiling of Candida auris Reveals Novel Insights into Biofilm-Mediated Resistance

Candida auris has emerged as a significant global nosocomial pathogen. This is primarily due to its antifungal resistance profile but also its capacity to form adherent biofilm communities on a range of clinically important substrates. While we have a comprehensive understanding of how other Candida species resist and respond to antifungal challenge within the sessile phenotype, our current understanding of C. auris biofilm-mediated resistance is lacking. In this study, we are the first to perform transcriptomic analysis of temporally developing C. auris biofilms, which were shown to exhibit phase- and antifungal class-dependent resistance profiles. A de novo transcriptome assembly was performed, where sequenced sample reads were assembled into an ~11.5-Mb transcriptome consisting of 5,848 genes. Differential expression (DE) analysis demonstrated that 791 and 464 genes were upregulated in biofilm formation and planktonic cells, respectively, with a minimum 2-fold change. Adhesin-related glycosylphosphatidylinositol (GPI)-anchored cell wall genes were upregulated at all time points of biofilm formation. As the biofilm developed into intermediate and mature stages, a number of genes encoding efflux pumps were upregulated, including ATP-binding cassette (ABC) and major facilitator superfamily (MFS) transporters. When we assessed efflux pump activity biochemically, biofilm efflux was greater than that of planktonic cells at 12 and 24 h. When these were inhibited, fluconazole sensitivity was enhanced 4- to 16-fold. This study demonstrates the importance of efflux-mediated resistance within complex C. auris communities and may explain the resistance of C. auris to a range of antimicrobial agents within the hospital environment.IMPORTANCE Fungal infections represent an important cause of human morbidity and mortality, particularly if the fungi adhere to and grow on both biological and inanimate surfaces as communities of cells (biofilms). Recently, a previously unrecognized yeast, Candida auris, has emerged globally that has led to widespread concern due to the difficulty in treating it with existing antifungal agents. Alarmingly, it is also able to grow as a biofilm that is highly resistant to antifungal agents, yet we are unclear about how it does this. Here, we used a molecular approach to investigate the genes that are important in causing the cells to be resistant within the biofilm. The work provides significant insights into the importance of efflux pumps, which actively pump out toxic antifungal drugs and therefore enhance fungal survival within a variety of harsh environments.

Collaborative investigation of variables in susceptibility testing of yeasts

A multicenter study was performed to evaluate the effect of medium, incubation time (24 and 48 h), and temperature (30 and 35 degrees C) on intra- and interlaboratory variations in MICs of flucytosine, amphotericin B, and ketoconazole for yeasts. Testing was performed on coded isolates of Candida species (11 strains) and Cryptococcus neoformans (2 strains) by using a standard macrodilution protocol 11 laboratories. Four chemically defined media buffered to pH 7.0 with morpholinepropanesulfonic acid were evaluated, including buffered yeast nitrogen base, synthetic amino acid medium-fungal, RPMI 1640 medium, and high-resolution antifungal assay medium. Intralaboratory variability was less than or equal to fourfold for 97% of the replicate sets of data. The highest level of interlaboratory agreement, irrespective of antifungal agent or incubation conditions, was observed with RPMI 1640 medium. Intralaboratory variability was less than or equal to fourfold for 93% of the determinations with ketoconazole and 100% with flucytosine tested in RPMI 1640 medium at 35 degrees C for 24 h. Variability in amphotericin B results was less than or equal to fourfold for 81% of the determinations in RPMI 1640 medium at 35 degrees C for 48 h. The rank order of MICs within each antifungal test group was similar among the various laboratories and was generally in agreement with the reference rank order regardless of the test medium that we used.

Efficacy of the anti-Candida rAls3p-N or rAls1p-N vaccines against disseminated and mucosal candidiasis

We have shown that vaccination with the recombinant N terminus of Als1p (rAls1p-N) protects mice against disseminated and oropharyngeal candidiasis. We now report that vaccination of mice with a related candidate, rAls3p-N, induces a broader antibody response than rAls1p-N and a similar cell-mediated immune response. The rAls3p-N vaccine was equally as effective as rAls1p-N against disseminated candidiasis but was more effective than rAls1p-N against oropharyngeal or vaginal candidiasis. Antibody titers did not correlate with protection against disseminated candidiasis, but delayed-type hypersensitivity did. The rAls3p-N vaccine is a promising new vaccine candidate for further exploration to prevent systemic and mucosal candidal infections.

Candida dubliniensis: phylogeny and putative virulence factors

Candida dubliniensis is a recently identified species which is implicated in oral candidosis in HIV-infected and AIDS patients. The species shares many phenotypic characteristics with, and is phylogenetically closely related to, Candida albicans. In this study the phylogenetic relationship between these two species was investigated and a comparison of putative virulence factors was performed. Four isolates of C. dubliniensis from different clinical sources were chosen for comparison with two reference C. albicans strains. First, the distinct phylogenetic position of C. dubliniensis was further established by the comparison of the sequence of its small rRNA subunit with representative Candida species. The C. dubliniensis isolates formed true unconstricted hyphae under most induction conditions tested but failed to produce true hyphae when induced using N-acetylglucosamine. Oral C. dubliniensis isolates were more adherent to human buccal epithelial cells than the reference C. albicans isolates when grown in glucose and equally adherent when grown in galactose. The C. dubliniensis isolates were sensitive to fluconazole, itraconazole, ketoconazole and amphotericin B. Homologues of seven tested C. albicans secretory aspartyl proteinase (SAP) genes were detected in C. dubliniensis by Southern analysis. In vivo virulence assays using a systemic mouse model suggest that C. dubliniensis is marginally less virulent than C. albicans. These data further confirm the distinct phenotypic and genotypic nature of C. dubliniensis and suggest that this species may be particularly adapted to colonization of the oral cavity.