Prevalence of Candida dubliniensis isolates in a yeast stock collection

Detection of Candida dubliniensis in oropharyngeal samples from human immunodeficiency virus infected and non-infected patients and in a yeast culture collection

The incidence of Candida dubliniensis in oropharyngeal swabs of 132 human immunodeficiency virus (HIV)-positive and 89 HIV-negative patients was determined. The samples were plated onto CHROMagar Candida medium and 82 strains, presumptively identified as C. albicans or C. dubliniensis, were further investigated (temperature test, chlamydoconidia production, specific primer PCR). In addition, 487 collection strains (isolated from clinical samples and previously identified as C. albicans on the basis of a positive germ tube test) were screened in order to identify C. dubliniensis isolates. Two C. dubliniensis strains were isolated from two HIV-positive patients without oral candidiasis. Candida dubliniensis was not isolated from 89 HIV-negative patients nor was it identified among the collection strains.

Evaluation of a rapid immunochromatographic assay for identification of Candida albicans and Candida dubliniensis

Candida dubliniensis was first established as a novel yeast species in 1995. It is particularly associated with recurrent episodes of oral candidosis in human immunodeficiency virus (HIV)-infected patients, but it has also been detected at other anatomical sites and at a low incidence level in non-HIV-infected patients. It shares so many phenotypic characteristics with C. albicans that it is easily misidentified as such. No rapid, simple, and commercial test that allows differentiation between C. dubliniensis and C. albicans has been developed, until now. Accurate species identification requires the use of genotype-based techniques that are not routinely available in most clinical microbiology diagnostic laboratories. The present study was designed to evaluate the efficiency of a new test (the immunochromatographic membrane [ICM] albi-dubli test; SR2B, Avrille, France) to differentiate between C. albicans and C. dubliniensis. The organisms evaluated were strains whose identities had previously been confirmed by PCR tests and freshly isolated clinical strains and included 58 C. albicans isolates, 60 C. dubliniensis isolates, and 82 isolates belonging to other species of yeast. The ICM albi-dubli test is based on the principle of immunochromatographic analysis and involves the use of two distinct monoclonal antibodies that recognize two unrelated epitopes expressed by both species or specific to only one species. The assay requires no complex instrumentation for analysis and can be recommended for routine use in clinical microbiology laboratories. Results are obtained within 2 h and 30 min and are easy to interpret. This evaluation demonstrated the good performance of this immunochromatographic test for C. albicans and C. dubliniensis isolated on Sabouraud dextrose agar, CHOROMagar Candida, and CandidaSelect, with sensitivities and specificities ranging from 93.1 to 100%. These parameters decreased, however, to 91.4% when the test was performed with yeast isolated with Candida ID.

Phenotypic and molecular characterization of Candida dubliniensis isolates from clinical specimens in Kuwait

OBJECTIVE

This study was carried out to characterize Candida dubliniensis using phenotypic and molecular methods and to determine the occurrence of C. dubliniensis in clinical specimens in Kuwait.

MATERIALS AND METHODS

A total of 880 clinical specimens for isolation of fungi were processed according to standard procedures. Of these, 390 germ-tube-positive clinical isolates of Candida species were examined for rough colonies with hyphal fringes and chlamydospore production on simplified sunflower seed agar for their presumptive phenotypicidentification as C. dubliniensis. The identification of C. dubliniensis isolates was further confirmed by the Vitek 2 yeast identification system, semi-nested (sn) PCR amplification of high-copy rDNA and direct DNA sequencing of the internally transcribed spacer 2 (ITS2) region.

RESULTS

Of the 390 isolates of Candida species investigated, 12 were identified as C. dubliniensis, giving an overall occurrence of 3%. All the C. dubliniensis isolates formed rough colonies with hyphal fringes and abundant chlamydospores on sunflower seed agar, did not assimilate trehalose, lactate and alpha-methyl-D-glucoside, and were isolated from human immunodeficiency virus (HIV)-negative patients. Four C. dubliniensis isolates utilized D-xylose. The species-specific primer derived from the ITS2 sequence of C. dubliniensis and used together with the panfungal reverse primer in the reamplification step of the snPCR specifically amplified rDNA from reference and clinical C. dubliniensis isolates and not from C. albicans or other Candida species. The identity of two representative isolates was confirmed by DNA sequencing of the ITS2 region.

CONCLUSIONS

The identity of 12 C. dubliniensis isolates was first established by phenotypic characteristics and then by snPCR using species-specific primers derived from ITS2 sequences. The recovery of C. dubliniensis from HIV-negative patients from Kuwait reinforces the existing view that this novel yeast species has a worldwide distribution and its occurrence is not restricted to any particular immunocompromised population.

Comparison of standard phenotypic assays with a PCR method to discriminate Candida albicans and C. dubliniensis

In 1995, Candida dubliniensis was described as a new species in the genus Candida. Its close relationship to C. albicans has proved problematic in the identification of C. dubliniensis in clinical specimens. The objective of this study was to determine if reproducible differentiation between both species can be obtained by phenotypic assays. Therefore, 100 strains from 86 patients with the ability to produce chlamydospores were examined with different methods including API ID 32 C, colour development on CHROMagar, chlamydospore formation on Staib agar, growth at different temperatures and germ tube formation at 39 degrees C. Additionally, polymerase chain reaction (PCR) was used as gold standard. Six of the investigated strains were C. dubliniensis. The results suggest that there is still no single phenotypic method satisfactory to distinguish between C. albicans and C. dubliniensis.

Comparison of phospholipase and proteinase activity in Candida albicans and C. dubliniensis

Although the production of virulence enzymes by Candida albicans has been extensively explored, little attention has been given to the virulence factors of C. dubliniensis. In the present study, an attempt was made to investigate phospholipase activity (Pz value) and secretory aspartyl proteinase production of C. dubliniensis and compare it with C. albicans. None of the 87 C. dubliniensis isolates tested, produced phosholipases whereas, in contrast all the 52 (100%) C. albicans isolates tested demonstrated varying degree of phospholipase activity (Pz value: 0.37-0.74), with 35 (67.3%) of them eliciting a higher phospholipase activity (Pz values between 0.37 and 0.50). Only 32% of the C. dubliniensis isolates exhibited moderate activity (score of 1+) of secretory aspartyl proteinase whereas a vast majority (68%) of them were non-proteolytic. On the contrary, a strong proteinase activity (score of 2+) was observed for 79% of C. albicans while the remaining 21% isolates showed moderate proteinase activity (score of 1+). As phospholipases and aspartyl proteinases of C. albicans are considered important virulence factors, the absence or lowered expression of these enzymes in C. dubliniensis may indicate the less virulent nature of this novel yeast species when compared with C. albicans.

Candida carriage and Candida dubliniensis in oropharyngeal samples of type-1 diabetes mellitus patients

The carriage of Candida dubliniensis in the oral cavities of type-1 diabetic patients were investigated. Of 230 patients 81 (35%) had Candida spp. in their oral cavity; C. albicans was the most frequently isolated species (58%). No C. dubliniensis was found in the study population.

Prevalence of Candida dubliniensis among the stored vaginal Candida isolates in a Turkish hospital. Pravalenz von Candida dubliniensis in gesammelten vaginalen Candida-Isolaten eines turkischen Krankenhanses

In this study, 600 stored Candida species, isolated from vaginal samples of immunocompetent women, and phenotypically identified as C. albicans on the basis of a positive germ tube test, were screened for the presence of C. dubliniensis by three phenotypical methods. Only one strain (0.17%) failed to grow at 45 degrees C, and produced abundant chlamydospores on both the cornmeal-Tween 80 agar and the Staib agar. This strain was identified as C. dubliniensis by using the ID-32C kit (bioMerieux Vitek) and confirmed by DNA sequencing of internal transcript spacer (ITS) region.

Tobacco agar, a new medium for differentiating Candida dubliniensis from Candida albicans

Isolates of Candida dubliniensis may be misidentified as Candida albicans in microbiological laboratories if only the germ tube and/or the chlamydospore test is used for identification to the species level. In this study, we have evaluated the efficacy of tobacco agar for the differentiation of C. dubliniensis from C. albicans. On this medium at 28 degrees C, all 30 C. dubliniensis isolates produced yellowish-brown colonies with hyphal fringes and abundant chlamydospores, whereas 54 C. albicans isolates formed smooth, white-to-cream-colored colonies with no chlamydospore production. This medium provides a simple tool for presumptive differentiation of C. dubliniensis from C. albicans.

Simplified sunflower (Helianthus annuus) seed agar for differentiation of Candida dubliniensis from Candida albicans

This study evaluated sunflower (Helianthus annuus) seed agar (SSA) for differentiation of Candida dubliniensis from Candida albicans on the basis of colony characteristics and chlamydospore production. Simplified SSA without creatinine and KH(2)PO(4) was also used. On both media, C. dubliniensis isolates (n = 25) developed rough colonies and formed abundant chlamydospores after incubation for 24-48 h at 28 degrees C, while C. albicans isolates (n = 53) showed smooth colonies with no evidence of chlamydospore formation. Cryptococcus neoformans isolates (n = 10) formed brown colonies on both media. Simplified SSA offers a simple and inexpensive tool for presumptive differentiation of C. dubliniensis from C. albicans in clinical microbiology laboratories.

Isolation and molecular identification of Candida dubliniensis from non-human immunodeficiency virus-infected patients in Kuwait

Candida dubliniensis is an emerging pathogen capable of causing oropharyngeal, vaginal and bloodstream infections. Although C. dubliniensis is similar to Candida albicans in several phenotypic characteristics, it differs from it with respect to epidemiology, certain virulence factors and the ability to develop resistance to fluconazole rapidly. In this study, the first seven isolations of C. dubliniensis from Kuwait are described, all originating from non-human immunodeficiency virus (HIV)-infected patients. The isolates were initially identified by the Vitek 2 yeast identification system, positive germ tube test, production of rough colonies and chlamydospores on Staib agar and by their inability to assimilate xylose, trehalose or methyl alpha-D-glucoside. The species identity of the isolates was subsequently confirmed by specific amplification of rDNA targeting the internally transcribed spacer 2 (ITS2), restriction endonuclease digestion of the amplified DNA and direct DNA sequencing of the ITS2. Using the E-test method, the MICs of C. dubliniensis test isolates were in the range 0.125-0.75 microg ml(-1) for fluconazole, 0.002-0.75 microg ml(-1) for itraconazole, 0.006-0.125 microg ml(-1) for ketoconazole, 0.002-0.5 microg ml(-1) for amphotericin B and 0.002-0.016 microg ml(-1) for voriconazole. Two of the isolates were resistant to 5-flucytosine (>32 microg ml(-1)), but none against fluconazole. The study reinforces the current view that C. dubliniensis has a much wider geographical and epidemiological distribution.

Prevalence of Candida dubliniensis among germ tube-positive yeasts recovered from the respiratory specimens in HIV-negative patients. Der Anteil von Candida dubliniensis bei keimschlauchpositiven Hefen in Untersuchungsproben aus dem Respirationstrakt HIV-negativer Patienten

The present investigation was conducted to identify Candida dubliniensis, from respiratory specimens, recovered from HIV-negative patients. Over a 7-month period, 75 germ tube and chlamydospore-positive yeasts were screened for C. dubliniensis, using a variety of phenotypic characteristics. Their identification was based on sugar assimilation reactions using API 20 C Aux. A total of seven (9%) isolates recovered from sputum, bronchial lavage and nasopharyngeal aspirate were identified as C. dubliniensis. All the isolates were susceptible to amphotericin B. One isolate each showed resistance to fluconazole and ketoconazole, and two were resistant to itraconazole. A significantly high percentage (43%) of C. dubliniensis showed resistance to flucytosine.

Comparison of the epidemiology, drug resistance mechanisms, and virulence of and

Candida dubliniensis is a pathogenic yeast species that was first identified as a distinct taxon in 1995. Epidemiological studies have shown that C. dubliniensis is prevalent throughout the world and that it is primarily associated with oral carriage and oropharyngeal infections in human immunodeficiency virus (HIV)-infected and acquired immune deficiency syndrome (AIDS) patients. However, unlike Candida albicans, C. dubliniensis is rarely found in the oral microflora of normal healthy individuals and is responsible for as few as 2% of cases of candidemia (compared to approximately 65% for C. albicans). The vast majority of C. dubliniensis isolates identified to date are susceptible to all of the commonly used antifungal agents, however, reduced susceptibility to azole drugs has been observed in clinical isolates and can be readily induced in vitro. The primary mechanism of fluconazole resistance in C. dubliniensis has been shown to be overexpression of the major facilitator efflux pump Mdr1p. It has also been observed that a large number of C. dubliniensis strains express a non-functional truncated form of Cdr1p, and it has been demonstrated that this protein does not play a significant role in fluconazole resistance in the majority of strains examined to date. Data from a limited number of infection models reflect findings from epidemiological studies and suggest that C. dubliniensis is less pathogenic than C. albicans. The reasons for the reduced virulence of C. dubliniensis are not clear as it has been shown that the two species express a similar range of virulence factors. However, although C. dubliniensis produces hyphae, it appears that the conditions and dynamics of induction may differ from those in C. albicans. In addition, C. dubliniensis is less tolerant of environmental stresses such as elevated temperature and NaCl and H(2)O(2) concentration, suggesting that C. albicans may have a competitive advantage when colonising and causing infection in the human body. It is our hypothesis that a genomic comparison between these two closely-related species will help to identify virulence factors responsible for the far greater virulence of C. albicans and possibly identify factors that are specifically implicated in either superficial or systemic candidal infections.

Molecular mechanisms of itraconazole resistance in Candida dubliniensis

It has previously been shown that overexpression of the CdMDR1 gene is a major contributor to resistance in fluconazole-resistant isolates of Candida dubliniensis. However, since CdMdr1p does not mediate transport of other azole drugs such as itraconazole, we investigated the molecular mechanisms of stable resistance to itraconazole obtained in three strains of C. dubliniensis (two with nonfunctional CdCDR1 genes and one with functional CdCDR1 genes) by serial exposure to this antifungal agent in vitro. Seven derivatives that were able to grow on agar medium containing 64 micro g of itraconazole per ml were selected for detailed analysis. These derivatives were resistant to itraconazole, fluconazole, and ketoconazole but were not cross resistant to inhibitors. CdMDR1 expression was unchanged in the seven resistant derivatives and their parental isolates; however, all seven derivatives exhibited increased levels of CdERG11 expression, and six of the seven derivatives exhibited increased levels of CdCDR1 expression compared to the levels of expression by their respective parental isolates. Except for one derivative, the level of rhodamine 6G efflux was decreased in the itraconazole-resistant derivatives compared to the level of efflux in their parental isolates, suggesting altered membrane properties in these derivatives. Analysis of their membrane sterol contents was consistent with a defective sterol C5,6-desaturase enzyme (CdErg3p), which was confirmed by the identification of mutations in the alleles (CdERG3) encoding this enzyme and their lack of functional complementation in a Saccharomyces cerevisiae erg3 mutant. The results of this study show that the loss of function of CdErg3p was the primary mechanism of in vitro-generated itraconazole resistance in six of the seven the C. dubliniensis derivatives. However, the mechanism(s) of itraconazole resistance in the remaining seventh derivative has yet to be determined.

Candida dubliniensis infections in a pediatric population: retrospective identification from clinical laboratory isolates of Candida albicans

Candida dubliniensis is a recently described species that shares many phenotypic and morphological features with Candida albicans. The clinical significance of isolating C. dubliniensis from the pediatric population is not clear, as most clinical isolates have been recovered from the oral cavities or bloodstreams of adults infected with human immunodeficiency virus. In order to understand further the epidemiology of C. dubliniensis in our pediatric population, we identified C. dubliniensis isolates from clinical isolates previously identified in the laboratory as C. albicans and conducted a retrospective chart review of cases of C. dubliniensis infections. A total of 205 isolates from 183 patients were tested, and only 14 (6.8%) were identified as C. dubliniensis. In 5 of the 14 positive cultures, C. dubliniensis was the sole organism isolated (two respiratory tract specimens, one tongue specimen, one vaginal specimen, and one skin specimen). A case review showed that there were no adverse outcomes for any of the patients, and only one of the patients with cultures positive for C. dubliniensis was immunocompromised. In our pediatric population, the distinction of C. dubliniensis from C. albicans did not prove to have significant clinical relevance. Data from further investigations may help to define better the role of C. dubliniensis as a potential pathogen in children.

Isolation of Candida dubliniensis in an aboriginal community in Ontario, Canada

This study reports the first isolation of Candida dubliniensis from North American Indians. Of 39 healthy human hosts sampled, two had C. dubliniensis. Genotypic analysis identified polymorphisms in these strains and differences from two reference strains. Our results suggest that yeast populations from indigenous communities in North America may be unique.

Candida dubliniensis identification in Brazilian yeast stock collection

We investigated the presence of Candida dubliniensis among isolates previously identified as Candida albicans and maintained in a yeast stock collection from 1994 to 2000. All isolates were serotyped and further evaluated for antifungal susceptibility profile. After doing a screening test for C. dubliniensis isolates based on the capability of colonies to grow at 42 C, its final identification was obtained by randomly amplified polymorphic DNA (RAPD) analysis using three different primers. A total of 46 out of 548 screened isolates did not exhibit growth at 42 C and were further genotyped by RAPD. Eleven isolates were identified as C. dubliniensis with RAPD analysis. Regarding serotypes, 81.5% of C. albicans and all C. dubliniensis isolates belonged to serotype A. Of note, 9 out of 11 C. dubliniensis isolates were obtained from patients with acquired immunodeficiency syndrome (Aids) and all of them were susceptible to azoles and amphotericin B. We found 17 (3%) C. albicans isolates that were dose-dependent susceptibility or resistant to azoles. In conclusion, we found a low rate of C. dubliniensis isolates among stock cultures of yeasts previously identified as C. albicans. Most of these isolates were recovered from oral samples of Aids patients and exhibited high susceptibility to amphotericin B and azoles. C. albicans serotype A susceptible to all antifungal drugs is the major phenotype found in our stock culture.

Candida dubliniensis at a university hospital in Saudi Arabia

Candida dubliniensis is a newly described yeast species that is a close phylogenetic relative of C. albicans. Although it has been reported from different parts of the world, no detailed investigation of this species has been done in Saudi Arabia. The purpose of the present study was to identify C. dubliniensis isolates recovered from clinical specimens at a tertiary-care hospital in Riyadh, Saudi Arabia, and to determine the drug susceptibility profiles of those isolates. Over a period of 8 months, 823 germ tube- and chlamydospore-positive yeasts identified as C. albicans and recovered from different clinical specimens were screened for their ability to grow at 45 degrees C on Sabouraud dextrose agar. Isolates which failed to grow at 45 degrees C were presumptively identified as C. dubliniensis. The species identities were further confirmed by the production of pseudohyphae and chlamydospores on Staib agar and their inability to assimilate D-xylose and alpha-methyl-D-glucoside by using the API 20C AUX system. A total of 27 (3.3%) isolates were identified as C. dubliniensis. They were all recovered from 23 human immunodeficiency virus-negative patients. The prevalence of C. dublinensis in bronchoalveolar lavage (33.3%), oral (16.7%), and blood (16.7%) specimens was high. In addition, 33 isolates previously identified as C. albicans and preserved among our stock blood culture isolates were also recruited for the study. Of these, 5 isolates were found to be C. dubliniensis, thus making the total number of isolates identified as this species 32. Antifungal susceptibility testing of the C. dubliniensis isolates showed 100% sensitivity to amphotericin B, 97% sensitivity to each of fluconazole and ketoconazole, and 87.5% sensitivity to itraconazole. However, in contrast to other studies, the majority of the isolates (65.6%) showed high levels of resistance to flucytosine (MIC > 64 microg/ml). Further studies are warranted to investigate the cause of this unusually high rate of resistance to flucytosine of the C. dubliniensis isolates in this region.

Racial distribution of Candida dubliniensis colonization among South Africans

Candida dubliniensis is a yeast species that has only recently been differentiated from Candida albicans. C. dubliniensis colonization was initially associated with human immunodeficiency virus (HIV)-positive individuals. Because of the large proportion of AIDS patients in South Africa, we tested the generality of this association by assessing the prevalence of C. dubliniensis colonization among 253 black HIV-positive individuals, 66 healthy black individuals, 22 white HIV-positive individuals, and 55 healthy white individuals in South Africa carrying germ tube-positive yeasts in their oral cavities. Molecular fingerprinting with Ca3, a complex DNA fingerprinting probe specific for C. albicans, and Cd25, a complex DNA fingerprinting probe specific for C. dubliniensis, provides the first conclusive evidence of the existence of C. dubliniensis among South African clinical yeast isolates and reveals a higher relative prevalence of this species among white healthy individuals (16%) than among HIV-positive white individuals (9%), black healthy individuals (0%), and black HIV-positive individuals (1.5%). A cluster analysis separated South African C. dubliniensis isolates into two previously described groups, groups I and II, with the majority of isolates clustering in group I. Isolates from white healthy individuals exhibited a higher level of relatedness. A comparison of the C. dubliniensis isolates from South Africa with a general collection of C. dubliniensis isolates collected worldwide revealed no South Africa-specific clade, as has been demonstrated for C. albicans. These results suggest that in South Africa, C. dubliniensis carriage is influenced more by race than by HIV infection status.

Identification of chlamydospore-negative Candida albicans using CHROMagar Candida medium

This study was undertaken to evaluate the utility of CHROMagar Candida medium for the identification of chlamydospore-negative Candida albicans. A total of 60 isolates including 45 chlamydospore-negative C. albicans, 10 chlamydospore-positive C. albicans (positive controls) and five non-C. albicans (negative controls) were investigated. On the basis of germ tube test, assimilation of trehalose (Tre), glucosamine (GlcN), N-acetyl glucosamine (GlcNAc), secretory aspartyl production and serotyping, the 45 chlamydospore-negative C. albicans isolates were assigned to the reported three groups. Eighteen isolates showing positive germ tube test, negative for the assimilation of Tre, GlcN/GlcNAc, strong producers of proteinase (2+) and assigned to serotype B belonged to group I. Whereas, the isolates in group II and group III showed common characteristics including assimilation of Tre, GlcN/GlcNAc, moderate production of proteinase (1+) and were serotype A, except for the fact that group II isolates were germ tube positive and group III isolates were negative. Using CHROMagar Candida medium, all the 45 chlamydospore-negative and 10 positive control isolates were accurately identified on the basis of characteristic green color at 37 degrees C for 48 h of incubation. On the other hand at an optimum incubation temperature of 37 degrees C none of the non-C. albicans (negative controls) showed characteristic green color thus yielding a 100% sensitivity and specificity. Isolates in group-I showed a slow growth rate and no visible growth was observed at 24 h, whereas, groups II, III and the control isolates showed visible growth at 24 h. Besides differences in growth rates, these isolates also varied in their characteristic colony color which gradually changed over a period of time. The results of this study clearly suggest that CHROMagar Candida medium is not only a simple, reliable and cost effective method for the identification of chlamydospore-negative atypical C. albicans, but can also be used to differentiate various groups of chlamydospore-negative C. albicans.

Comparison of Candida dubliniensis and C. albicans based on polar lipid composition

AIMS

To test the hypothesis that strains of Candida dubliniensis and C. albicans can be differentiated on the basis of polar lipid profiles.

METHODS AND RESULTS

Five isolates of C. dubliniensis and six isolates of C. albicans were tested by growth at 45 degrees C, production of chlamydospores on cornmeal agar, colonial colour on CHROMagar Candida medium and assimilation of DL-lactate, alpha-methyl-D-glucoside and xylose. Polar lipids were then extracted from freeze-dried cultures and analysed using fast atom bombardment mass spectrometry. Isolates were grouped by single linkage clustering based on correlation coefficients for strain pairs calculated with carboxylate and phospholipid molecular species distributions. The most intense carboxylate and phospholipid molecular species anions were of m/z 281 (C(18 : 1)) and m/z 515 (PA 23 : 2). Phosphatidylethanolamine and phosphatidylglycerol were the predominant phospholipid families in C. dubliniensis, compared with phosphatidic acid in C. albicans isolates. All of the C. dubliniensis isolates grouped together in one cluster, whereas all of the C. albicans isolates grouped in a separate cluster.

CONCLUSIONS

Fast atom bombardment mass spectrometry can differentiate the two species based on analysis of polar lipid distributions.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings demonstrate that C. dubliniensis and C. albicans have distinct polar lipid profiles.

Evaluation of a method for identification of Candida dubliniensis bloodstream isolates

To evaluate methods for differentiating Candida albicans and Candida dubliniensis, 772 putative C. albicans bloodstream isolates were tested for growth at 37 and 42 degrees C. Isolates showing no growth at 42 degrees C, abundant chlamydospore production, and the sugar assimilation pattern of the type strain were confirmed by DNA-based procedures to be C. dubliniensis.

Microevolutionary changes and chromosomal translocations are more frequent at RPS loci in Candida dubliniensis than in Candida albicans

The Cd1 fingerprinting probe of Candida dubliniensis, which is extremely effective in identifying microevolutionary changes in infecting populations, generates hybridization patterns that are similar to those generated by the Candida albicans fingerprinting probe Ca3. Since Ca3 recognizes microevolutionary changes through the repeat sequence RPS, it was suggested that Cd1 also contains a RPS-like element. To test this possibility, the C. albicans RPS unit was used as a probe, and an RPS-like element, RPSd1, was cloned from C. dubliniensis. The sequence of RPSd1 was 76% homologous to that of the C. albicans RPS unit RPS620 and the organization, including the non-RPS 3' and 5' bordering sequences, was highly similar. This analysis revealed additional copies of the repeat extraalt element and short additional repeat (SAR) sequences in both RPSd1 and RPS620 not previously identified in the latter. This analysis has allowed us to develop a model of RPSd1 organization and to revise the model for RPS620 organization. An estimate of the average frequency of reorganization (duplication and deletion) per RPS unit in C. dubliniensis was similar to that for C. albicans, but the estimate of frequency of reorganization per C. dubliniensis genome was higher, most probably as a result of the higher estimated average number of RPS clusters in C. dubliniensis. These results demonstrate that the microevolutionary changes identified by the Cd1 fingerprinting probe are based on the reorganization of RPS-like elements and are, therefore, similar to the microevolutionary changes identified by the Ca3 probe of C. albicans. Linkage analysis of pairs of markers situated on either side of an RPS cluster on chromosome 7 further revealed frequent recombination between non-homologous chromosomes at the RPS cluster in C. dubliniensis strains, but not in C. albicans strains, suggesting that RPS clusters may function as recombination hot spots in C. dubliniensis.

Prevalence of Candida dubliniensis in the BCCM/IHEM Biomedical Fungi/Yeasts culture collection (isolates before 1990)

The BCCM/IHEM Biomedical Fungi/Yeasts collection hosts 1200 Candida albicans strains of the Vanbreuseghem mycotheque isolated between 1951 and 1997. From this collection, 469 freeze-dried C. albicans strains, producing chlamydospores, germ tubes and forming green colonies on CHROMagar, all isolated before 1990, were screened to identify the Candida dubliniensis isolates. Screening was performed in different steps using the growth at 45 degrees C, the assimilation of xylose, the intracellular beta-glucosidase activity test and C. dubliniensis-specific polymerase chain reaction (PCR) with primers from ACT1 intron sequence. Five isolates (1%) were identified as C. dubliniensis: one isolate was not documented, the others were of oropharyngeal origin of which two (1987 and 1990) were from proven human immunodeficiency virus patients.

Pathogenicity and virulence of Candida dubliniensis: comparison with C. albicans

Candida dubliniensis is a newly described fungus that is frequently isolated from the oral cavities of HIV-positive patients. Although extensive studies have been performed on the phylogeny of C. dubliniensis, little is known about the pathogenic ecology of this yeast. Here we examined aspects related to C. dubliniensis in comparison with those of C. albicans. When injected intravenously into mice, C. dubliniensis had a higher survival rate than C. albicans. Histopathological analysis disclosed that C. dubliniensis remained mostly in the yeast form in the infected organs, whereas C. albicans changed into the mycelial form. The host inflammatory reaction was aggressive with C. dubliniensis infection and mild with C. albicans infection. Co-culture of the yeasts with human polymorphonuclear leukocytes disclosed that C. dubliniensis is more vulnerable to the fungicidal activity of leukocytes than C. albicans. C. dubliniensis was also more susceptible to the toxic effect of hydrogen peroxide. When cultured in vitro, C. dubliniensis grew more slowly than C. albicans, but the formation of germ tubes was faster. When the fungi were cultured in RPMI 1640, a fetal bovine serum supplement suppressed the growth of C. dubliniensis but enhanced that of C. albicans. These results clearly indicated that C. dubliniensis is less virulence than C. albicans.

Molecular mechanisms of fluconazole resistance in Candida dubliniensis isolates from human immunodeficiency virus-infected patients with oropharyngeal candidiasis

Candida dubliniensis is a newly identified species of Candida that is phenotypically similar to but genetically distinct from C. albicans. This organism has been recovered with increasing frequency from the oral cavities of human immunodeficiency virus (HIV)-infected and AIDS patients and has been implicated as a causative agent of oral candidiasis and systemic disease. In the present study we characterized the molecular mechanisms of resistance to fluconazole (FLC) in C. dubliniensis clinical isolates from two different HIV-infected patients with oropharyngeal candidiasis. Isolates were identified to the species level by phenotypic and genotypic tests. DNA-typing techniques were used to assess strain identity. Antifungal susceptibility testing was performed by NCCLS techniques. Northern blotting analysis was used to monitor the expression of genes encoding lanosterol demethylase (ERG11) and efflux transporters (CDR and MDR1) in matched sets of C. dubliniensis-susceptible and -resistant isolates by using probes generated from their homologous C. albicans sequences. In addition, ERG11 genes were amplified by PCR, and their nucleotide sequences were determined in order to detect point mutations with a possible effect in the affinity for azoles. Decreasing susceptibilities to FLC were detected in C. dubliniensis isolates recovered from both patients during the course of treatment. FLC-resistant C. dubliniensis isolates from one patient demonstrated combined upregulation of the MDR1, CDR1, and ERG11 genes. Among the isolates from the second patient, all isolates showing decreased susceptibility to FLC demonstrated upregulation of MDR1, whereas the levels of mRNA for the ERG11 genes remained constant and the expression of CDR genes was negligible. Fourteen point mutations were found in the ERG11 genes of the isolates with decreased susceptibility to FLC. These data demonstrate that the development of azole resistance in C. dublinensis clinical isolates from HIV-infected patients treated with FLC is mediated by multiple molecular mechanisms of resistance, similar to the observations found in the case of C. albicans.

Hypertonic sabouraud broth as a simple and powerful test for Candida dubliniensis screening

We developed a new screening test for C. dubliniensis based on its inability to grow on Sabouraud dextrose broth with 6.5% NaCl. A total of 266 clinical yeast isolates and 3 reference strains were tested, including 250 C. albicans and 19 C. dubliniensis strains. All C. albicans isolates tested exhibited significant growth on hypertonic Sabouraud broth up to 96 h, while, all C. dubliniensis isolates did not exhibit any visually detectable growth during the same period.

Clonality structure in Candida dubliniensis

Multilocus enzyme electrophoresis was performed on 76 European strains of Candida dubliniensis. Ten of the 20 enzyme-encoding loci were polymorphic, giving rise to 10 electrophoretic types within the sample studied. Investigation of the population genetics of a subset of 36 strains from HIV-infected patients in London showed the existence of strong heterozygote deficits and excesses associated with significant linkage disequilibria between pairs of loci. These findings, together with the predominance of multilocus genotypes, strongly suggest that C. dubliniensis is mainly (if not totally) clonal. Analysis of genotypes of a larger number of strains should confirm this conclusion and improve our understanding of the epidemiology of this pathogen.

Prevalence of yeasts in saliva and root canals of teeth associated with apical periodontitis

AIMS

To determine: (i) the relative prevalence and diversity of yeasts in salivary and root canal samples from the same patients; and (ii) the clinical factors associated with their presence in saliva and root canals.

METHODOLOGY

Sixty root canal samples from teeth associated apical periodontitis and the corresponding whole unstimulated saliva samples were obtained from 55 patients. The medical history including antibiotic therapy and clinical/radiographic data on the teeth were recorded. The samples were serially diluted and cultured on yeast & fungi-selective sabouraud dextrose agar. Isolates were characterized and speciated by the germ tube formation test, hyphal morphology and a commercial biochemical test kit (Rapid ID32C(R) system).

RESULTS

Twenty-three yeast isolates were recovered from 19 saliva samples and eight isolates from six root canal samples. Candida albicans (17/23 & 3/8) and Rodotorula mucilaginosa (2/23 & 4/8) were the most prevalent isolates from saliva and root canal samples. It was significantly (13.8 times) more probable that yeasts would be recovered from root canals when they were also present in the saliva (P = 0.021). The effect of coronal restoration leakage (P = 0.08) and previous root canal treatment (P = 0.123) were equivocal. The history of antibiotic therapy had no association with the presence of yeasts in saliva (OR = 1.1).

CONCLUSIONS

Yeasts occurred relatively infrequently (10%) in root canals. Their presence in root canals was significantly associated with their presence in saliva. The role of yeasts in the initiation and perpetuation of periapical disease remains to be determined.

Identification of Candida dubliniensis among oral yeast isolates from an Italian population of human immunodeficiency virus-infected (HIV+) subjects

Candida dubliniensis, an emerging oral pathogen, phenotypically resembles Candida albicans so closely that it is easily misidentified as such. The aim of the present study was to evaluate the usefulness of two phenotypic methods, growth at 45 degrees C and 2,3,5-triphenyltetrazolium chloride (TTC) reduction, for confirming presumptive identification of C. dubliniensis and C. albicans by colony color on CHROMagar Candida (CAC) medium. A combination of these methods was used to establish the prevalence of oral C. dubliniensis in an Italian population of 45 human immunodeficiency virus (HIV)-infected subjects. Twenty-two samples (48.9%) were positive for yeasts on CAC medium producing a total of 37 fungal isolates. The colony color and 45 degrees C growth ability test correctly identified all C. dubliniensis and C. albicans isolates (5/37, 13.5%, and 16/37, 43.2%, respectively), while assessment of TTC reduction misidentified one C. albicans isolate. The isolation rate of C. dubliniensis was 11.1% (5/45 patients). All of the C. dubliniensis isolates were highly susceptible to fluconazole (MIC = 0.5 microg/ml). The combination of CAC medium screening with growth at 45 degrees C and TTC reduction tests may represent a simple, reliable and inexpensive identification protocol for C. dubliniensis.

Oral yeast carriage in patients with advanced cancer

The aim of this study was to investigate oral yeast carriage amongst patients with advanced cancer. Oral rinse samples were obtained from 120 subjects. Yeasts were isolated using Sabouraud's dextrose agar and CHROMagar Candida, and were identified using a combination of the API 20 C AUX yeast identification system, species-specific PCR and 26S rDNA gene sequencing. Oral yeast carriage was present in 66% of subjects. The frequency of isolation of individual species was: Candida albicans, 46%; Candida glabrata, 18%; Candida dubliniensis, 5%; others, < 5%. The increasing isolation of non-Candida albicans species is clinically important, since these species are often more resistant to antifungal drugs. Oral yeast carriage was associated with denture wearing (P = 0.006), and low stimulated whole salivary flow rate (P = 0.009). Identification of these risk factors offers new strategies for the prevention of oral candidosis in this group of patients.

Candida dubliniensis fungemia and vascular access infection

Candida dubliniensis is a newly recognized species of yeast, which may have been forrmerly identified as Candida albicans, that has been rarely isolated from invasive fungal infections among humans. The authors document a C. dubliniensis fungemia that occurred during the course of a vascular access infection in a 2-year-old who was undergoing active therapy for neuroblastoma. Presumptive C. albicans isolates from an 18-year period were reassessed, and it was found that C. dubliniensis is a rare cause of fungemia among pediatric patients (0.5% of all such isolates).

Multicenter prospective surveillance of oral Candida dubliniensis among adult Brazilian human immunodeficiency virus-positive and AIDS patients

The incidence of C. dubliniensis in South America has not yet been determined. In the present study, oral swab samples were taken from 108 HIV-infected/AIDS individuals attending 6 separate Brazilian HIV-treatment centers to determine the incidence of C. dubliniensis in this population. Swabs were plated onto CHROMagar Candida medium and 155 isolates, presumptively identified as C. albicans or C. dubliniensis were further investigated. In a preliminary screen for C. dubliniensis, 13 of the 155 isolates showed no or poor growth at 42 degrees C, and all them were subjected to randomly amplified polymorphic DNA (RAPD) and polymerase chain reaction (PCR) analysis using C. dubliniensis-specific primers. We confirmed that 4 out of 13 isolates were C. dubliniensis, representing an incidence rate of 2.8% for the Brazilian HIV-infected population infected with yeasts exhibiting green colonies on CHROMagar Candida. This value is significantly lower than those reported in Ireland and the United States.

Biofilm formation by Candida dubliniensis

Candida dubliniensis is an opportunistic yeast closely related to Candida albicans that has been recently implicated in oropharyngeal candidiasis in human immunodeficiency virus-infected patients. Most manifestations of candidiasis are associated with biofilm formation, with cells in biofilms displaying properties dramatically different from free-living cells grown under normal laboratory conditions. Here, we report on the development of in vitro models of C. dubliniensis biofilms on the surfaces of biomaterials (polystyrene and acrylic) and on the characteristics associated with biofilm formation by this newly described species. Time course analysis using a formazan salt reduction assay to monitor metabolic activities of cells within the biofilm, together with microscopy studies, revealed that biofilm formation by C. dubliniensis occurred after initial focal adherence, followed by growth, proliferation, and maturation over 24 to 48 h. Serum and saliva preconditioning films enhanced the initial attachment of C. dubliniensis and subsequent biofilm formation. Scanning electron microscopy and confocal scanning laser microscopy were used to further characterize C. dubliniensis biofilms. Mature C. dubliniensis biofilms consisted of a dense network of yeasts cells and hyphal elements embedded within exopolymeric material. C. dubliniensis biofilms displayed spatial heterogeneity and an architecture showing microcolonies with ramifying water channels. Antifungal susceptibility testing demonstrated the increased resistance of sessile C. dubliniensis cells, including the type strain and eight different clinical isolates, against fluconazole and amphotericin B compared to their planktonic counterparts. C. dubliniensis biofilm formation may allow this species to maintain its ecological niche as a commensal and during infection with important clinical repercussions.

Rapid identification of candida species by TaqMan PCR

AIM

To develop and evaluate a TaqMan(TM) polymerase chain reaction (PCR) for the rapid identification and speciation of candida species.

METHODS

Species specific primer and probe sets were designed for the identification of Candida albicans, C. parapsilosis, C. tropicalis, C. krusei, C. kefyr, and C. glabrata from clinical isolates in a 5' exonuclease (TaqMan(TM)) assay. The probes were labelled with three fluorescent dyes to enable differentiation between species when three primer and probe sets were combined in two multiplexes. The specificity of these assays was evaluated against a range of National Collection of Pathogenic Fungi strains, clinical isolates of yeast, bacterial and viral pathogens.

RESULTS

The primer and probe sets have been shown to be 100% specific for their respective species; there was no crossreaction between any set and human DNA, or extracts from other candida species, fungal, bacterial, or viral pathogens tested. Extracts from two clinical isolates, originally identified as C albicans on the basis of germ tube formation, were not amplified by any of the primer and probe sets. These isolates have been putatively re-identified as C dubliniensis after sequencing of the variable internal transcribed spacer region ITS2 and lack of growth at 45 degrees C.

CONCLUSION

This TaqMan assay provides a rapid alternative to conventional culture based techniques for the identification and speciation of the most frequently isolated candida species. The simple extraction method followed by TaqMan PCR can identify the six species mentioned in four hours.

Candida dubliniensis at a cancer center

Candida dubliniensis, a germ tube-positive yeast first described and identified as a cause of oral candidiasis in patients with acquired immunodeficiency syndrome in Europe in 1995, has an expanding clinical and geographic distribution that appears to be similar to that of the other germ tube-positive yeast, Candida albicans. This study determined the frequency, clinical spectrum, drug susceptibility profile, and suitable methods for identification of this emerging pathogen at a cancer center in 1998 and 1999. Twenty-two isolates were recovered from 16 patients with solid-organ or hematologic malignancies or acquired immunodeficiency syndrome. Two patients with cancer had invasive infection, and 14 were colonized with fungus or had superficial fungal infection. All isolates produced germ tubes and chlamydospores at 37 degrees C, did not grow at 45 degrees C, and gave negative reactions with d-xylose and alpha-methyl-d-glucoside in the API 20 C AUX and ID 32 C yeast identification systems. Phenotypic identification was confirmed by molecular beacon probe technology. All isolates were susceptible to the antifungal drugs amphotericin B, 5-fluorocytosine, fluconazole, itraconazole, and ketoconazole.

Genotypic identification of Candida dubliniensis isolated from HIV patients by MLEE

Candida dubliniensis is a novel species only recently described. This emerging pathogen shares some of the phenotypic characteristics specific to C. albicans but is genetically different. In this study we typed four strains of atypical C. albicans isolated in our laboratory and compared them to 41 strains of C. albicans and 11 strains of C. dubliniensis by several phenotypic methods and by multilocus enzyme electrophoresis. Using factorial correspondence analysis, we distinguished C. dubliniensis and the atypical C. albicans strains from all strains of C. albicans. Atypical C. albicans strains were identified as C. dubliniensis.

Comparison of the hydrophobic properties of Candida albicans and Candida dubliniensis

Although Candida dubliniensis is a close genetic relative of Candida albicans, it colonizes and infects fewer sites. Nearly all instances of candidiasis caused by C. dubliniensis are restricted to the oral cavity. As cell surface hydrophobicity (CSH) influences virulence of C. albicans, CSH properties of C. dubliniensis were investigated and compared to C. albicans. Growth temperature is one factor which affects the CSH status of stationary-phase C. albicans. However, C. dubliniensis, similar to other pathogenic non-albicans species of Candida, was hydrophobic regardless of growth temperature. For all Candida species tested in this study (C. albicans, C. dubliniensis, C. glabrata, C. krusei, C. parapsilosis, and C. tropicalis), CSH status correlated with coaggregation with the anaerobic oral bacterium Fusobacterium nucleatum. Previous studies have shown that CSH status of C. albicans involves multiple surface proteins and surface protein N-glycans. The hydrophobic surface glycoprotein CAgp38 appears to be expressed by C. albicans constitutively regardless of growth temperature and medium. C. dubliniensis expresses a 38-kDa protein that cross-reacts with the anti-CAgp38 monoclonal antibody; however, expression of the protein was growth medium and growth temperature dependent. The anti-CAgp38 monoclonal antibody has been shown to inhibit adhesion of C. albicans to extracellular matrix proteins and to vascular endothelial cells. Since protein glycosylation influences the CSH status of C. albicans, we compared the cell wall mannoprotein content and composition between C. albicans and C. dubliniensis. Similar bulk compositional levels of hexose, phosphate, and protein in their N-glycans were determined. However, a component of the C. albicans N-glycan, acid-labile phosphooligomannoside, is expressed much less or negligibly by C. dubliniensis, and when present, the oligomannosides are predominantly less than five mannose residues in length. In addition, the acid-labile phosphooligomannoside profiles varied among the three strains of C. dubliniensis we tested, indicating the N-glycan of C. dubliniensis differs from C. albicans. For C. albicans, the acid-labile phosphooligomannoside influences virulence and surface fibrillar conformation, which affects exposure of hydrophobic surface proteins. Given the combined role in C. albicans of expression of specific surface hydrophobic proteins in pathogenesis and of surface protein glycosylation on exposure of the proteins, the lack of these virulence-associated CSH entities in C. dubliniensis could contribute to its limited ability to cause disseminated infections.

Differentiation of Candida dubliniensis from Candida albicans on staib agar and caffeic acid-ferric citrate agar

The methods currently available for the identification of the pathogenic yeast Candida dubliniensis all have disadvantages in that they are time-consuming, expensive, and/or, in some cases, unreliable. In a recent study (P. Staib and J. Morschhäuser, Mycoses 42:521-524; 1999) of 14 C. dubliniensis and 11 C. albicans isolates, it was suggested that the ability of C. dubliniensis to produce rough colonies and chlamydospores (chlamydoconidia) on Staib agar (SA) provided a simple means of differentiating it from its close relative C. albicans. In the present investigation, we examined the colony morphology and chlamydospore production of 130 C. dubliniensis and 166 C. albicans isolates on SA and on the related defined medium caffeic acid-ferric citrate agar (CAF). All of the C. dubliniensis and C. albicans isolates produced chlamydospores on the control medium, i.e., rice-agar-Tween agar. However, while none of the C. albicans isolates produced chlamydospores on either SA or CAF, 85.4 and 83.8% of the C. dubliniensis isolates produced chlamydospores on SA and CAF, respectively. All of the C. albicans isolates grew as smooth, shiny colonies on SA after 48 to 72 h of incubation at 30 degrees C, while 97.7% of the C. dubliniensis isolates grew as rough colonies, many (65%) with a hyphal fringe. In contrast, 87.4% of the C. albicans and 93.8% of the C. dubliniensis isolates yielded rough colonies on CAF. Although the results of this study confirm that SA is a good medium for distinguishing between C. dubliniensis and C. albicans, we believe that discrimination between these two species is best achieved on the basis of colony morphology rather than chlamydospore production.

Differentiation between Candida dubliniensis and Candida albicans by fatty acid methyl ester analysis using gas-liquid chromatography

Candida dubliniensis is often found in mixed culture with C. albicans, but its recognition is hampered as the color of its colonies in primary culture on CHROMagar Candida varies. Furthermore, definite identification of C. dubliniensis is difficult to achieve, time-consuming, and expensive. Therefore, a method to discriminate between these two closely related yeast species by fatty acid methyl ester (FAME) analysis using gas-liquid chromatography (Sherlock Microbial Identification System [MIS]; MIDI, Inc., Newark, Del.) was developed. Although the chromatograms of these two species revealed no obvious differences when applying FAME analysis, a new library (CADLIB) was successfully created using Sherlock Library Generation Software (MIDI). The amount and frequency of FAME was analyzed using library training files (n = 10 for each species), preferentially those comprising reference strains. For testing the performance of the CADLIB, clinical isolates genetically assigned to the respective species (C. albicans, n = 32; C. dubliniensis, n = 28) were chromatographically analyzed. For each isolate tested, MIS computed a similarity index (SI) indicating a hierarchy of possible strain fits. When using the newly created library CADLIB, the SIs for C. albicans and C. dubliniensis ranged from 0.11 to 0.96 and 0.53 to 0. 93 (for all but one), respectively. Only three isolates of C. albicans (9.4%) were misidentified as C. dubliniensis, whereas all isolates of C. dubliniensis were correctly identified. Resulting differentiation accuracy was 90.6% for C. albicans and 100% for C. dubliniensis. Cluster analysis and principal component analysis of the resulting FAME profiles showed two clearly distinguishable clusters matching up with two assigned species for the strains tested. Thus, the created library proved to be well suited to discriminate between these two species.

Phagocytosis, oxidative burst, and killing of Candida dubliniensis and Candida albicans by human neutrophils

Candida dubliniensis is a phylogenetically closely related species to Candida albicans. So far virtually nothing is known about the virulence factors of C. dubliniensis. Cell surface hydrophobicity (CSH) plays a critical role in adhesion of microorganisms to phagocytic cells; hydrophobic cells of C. albicans have been reported to be less sensitive to phagocytic killing than hydrophilic cells. C. dubliniensis displays CSH at 37 degrees C in contrast to C. albicans. To elucidate this issue, we determined levels of phagocytosis, oxidative burst and killing by human neutrophils of C. dubliniensis (n=10) compared to C. albicans (n=10) both cultured at 37 degrees C. Obtained test results revealed no statistically significant differences between these two yeast species for the level of phagocytosis (77.3 vs. 76.2% after 60 min), evoked oxidative burst (64.5 vs. 67.3% after 30 min) and killing (72.7 vs. 73.1% after 240 min). Therefore, human neutrophils can be considered to be equally efficient against these two yeast species.

Comparison of virulence factors of oral Candida dubliniensis and Candida albicans isolates in healthy people and patients with chronic candidosis

We determined differences in the expression of certain virulence factors between oral Candida dubliniensis and Candida albicans species. In addition, clonal differences were sought among C. albicans isolates recovered from patients with and without compromised immune system. The material comprised 93 clinical yeast isolates originated in 40 subjects (1-5 isolates per subject). All 26 C. dubliniensis isolates and 46 C. albicans isolates originated from healthy routine dental clinic patients. Additionally, 21 C. albicans isolates were collected from patients with autoimmune polyendocrinopathy-candidosis-ectodermal dystrophy (APECED), who have chronic candidosis as one manifestation of their immunocompromising disease. Polymerase chain reaction amplification using the random sequence primer OPE-03 enabled grouping of the C. dubliniensis isolates in 2 genotypes (I and II) and C. albicans isolates in 15 genotypes (I-XV). No significant difference was found in the distribution of genotypes between the patients with APECED and the healthy subjects. C. dubliniensis isolates exhibited high-frequency phenotypic switching significantly more frequently than did C. albicans isolates, and vice versa regarding phospholipase and proteinase production. Proteinase production was significantly more frequent among C. albicans genotype V than genotype IX isolates. No significant difference was found in expression of virulence factors of C. albicans isolates between the patients with APECED and the healthy subjects.

Retrospective identification and characterization of Candida dubliniensis isolates among Candida albicans clinical laboratory isolates from human immunodeficiency virus (HIV)-infected and non-HIV-infected individuals

Fungal opportunistic infections, and in particular those caused by the various Candida species, have gained considerable significance as a cause of morbidity and, often, mortality. The newly described species Candida dubliniensis phenotypically resembles Candida albicans so closely that it is easily misidentified as such. The present study was designed to determine the frequency at which this new species is not recognized in the clinical laboratory, to determine the patient populations with which C. dubliniensis is associated, to determine colonization versus infection frequency, and to assess fluconazole resistance. Over a 2-year period, 1,251 isolates that were initially identified as C. albicans by a hospital clinical laboratory were reevaluated for C. dubliniensis by inability to grow at 45 degrees C, colony color on CHROMagar Candida medium, coaggregation assay with Fusobacterium nucleatum, and sugar assimilation profiles (API 20C AUX yeast identification system). A total of 15 (1.2%) isolates from 12 patients were identified as C. dubliniensis. Ten of the patients were found to be immunocompromised (these included patients with human immunodeficiency virus infection or AIDS, cancer patients receiving chemotherapy, and patients awaiting transplantation). Thirteen isolates were highly susceptible to fluconazole (MIC, <0.5 microgram/ml). Three isolates from one patient, genotypically confirmed as the same strain, showed variable susceptibility to fluconazole. The first isolate was susceptible, whereas the other two isolates were dose-dependent susceptible (MIC, 16.0 microgram/ml). These data confirm the close association of C. dubliniensis with immunocompromised states and that increased fluconazole MICs may develop in vivo. This study emphasizes the importance of screening germ-tube-positive yeasts for the inability to grow at 45 degrees C followed by confirmatory tests in order to properly identify this species.

Identification of medically important yeasts using PCR-based detection of DNA sequence polymorphisms in the internal transcribed spacer 2 region of the rRNA genes

Identification of medically relevant yeasts can be time-consuming and inaccurate with current methods. We evaluated PCR-based detection of sequence polymorphisms in the internal transcribed spacer 2 (ITS2) region of the rRNA genes as a means of fungal identification. Clinical isolates (401), reference strains (6), and type strains (27), representing 34 species of yeasts were examined. The length of PCR-amplified ITS2 region DNA was determined with single-base precision in less than 30 min by using automated capillary electrophoresis. Unique, species-specific PCR products ranging from 237 to 429 bp were obtained from 92% of the clinical isolates. The remaining 8%, divided into groups with ITS2 regions which differed by </=2 bp in mean length, all contained species-specific DNA sequences easily distinguishable by restriction enzyme analysis. These data, and the specificity of length polymorphisms for identifying yeasts, were confirmed by DNA sequence analysis of the ITS2 region from 93 isolates. Phenotypic and ITS2-based identification was concordant for 427 of 434 yeast isolates examined using sequence identity of >/=99%. Seven clinical isolates contained ITS2 sequences that did not agree with their phenotypic identification, and ITS2-based phylogenetic analyses indicate the possibility of new or clinically unusual species in the Rhodotorula and Candida genera. This work establishes an initial database, validated with over 400 clinical isolates, of ITS2 length and sequence polymorphisms for 34 species of yeasts. We conclude that size and restriction analysis of PCR-amplified ITS2 region DNA is a rapid and reliable method to identify clinically significant yeasts, including potentially new or emerging pathogenic species.

Evaluation of phenotypic markers for selection and identification of Candida dubliniensis

Candida dubliniensis is often associated with C. albicans in cultures. Easy-to-perform selective isolation procedures for these closely related species do not exist. Therefore, we evaluated previously described discriminatory phenotypic markers for C. dubliniensis. A total of 150 oral rinses from human immunodeficiency virus (HIV)-infected patients were cultured on CHROMagar Candida. Dark green colonies described as being indicative of C. dubliniensis and other green colonies, 170 in total, were isolated. Chlamydospore formation, intracellular beta-D-glucosidase activity, ability to grow at 42 degrees C, carbohydrate assimilation pattern obtained by the API ID 32C, and Fourier transform infrared (FT-IR) spectroscopy were used for phenotypic characterization. Sequencing of the 5' end of the nuclear large-subunit (26S) ribosomal DNA gene was used for definitive species identification for C. dubliniensis. C. dubliniensis was found in 34% of yeast-colonized HIV-infected patients. The color of the colonies on CHROMagar Candida proved to be insufficient for selecting C. dubliniensis, since only 30 of 53 proven C. dubliniensis isolates showed a dark green color in primary cultures. The described typical chlamydospore formation can give only some indication of C. dubliniensis. The assimilation pattern proved to be insufficient to discriminate C. dubliniensis from C. albicans. All C. dubliniensis strains showed no or highly restricted growth at 42 degrees C and a lack of beta-D-glucosidase activity. Unfortunately, atypical C. albicans strains can also exhibit these phenotypic traits. FT-IR spectroscopy combined with hierarchical clustering proved to be as reliable as genotyping for discriminating the two species.

Candida dubliniensis fungemia: the first four cases in North America

We report the first four North American cases of Candida dubliniensis fungemia, including the first isolation of this organism from the bloodstream of an HIV-infected person. All isolates were susceptible in vitro to commonly used antifungal drugs. This report demonstrates that C. dubliniensis can cause bloodstream infection; however, the incidence of disease is not known.