Evaluation of six commercial systems for identification of medically important yeasts

Exploring the biomedical potential of a novel modified glass ionomer cement against the pandrug-resistant oral pathogen Candida albicans SYN-01

Dental caries is an infectious disease that is a major concern for dentists. Streptococci and Lactobacilli were long thought to be the primary etiology responsible for caries. Candida albicans with acidogenic and aciduric characteristics has recently been implicated in the onset and progression of cariogenic lesions. Moreover, due to the increased resistance to common antimicrobials, the discovery of innovative candidates is in high demand. Therefore, our study might be the first report that explores the efficacy of glass ionomer cement (GIC) incorporated with a newly modified carboxylated chitosan derivative (CS-MC) against multidrug-resistant (MDR) and/or pandrug resistant (PDR) C. albicans isolated from the oral cavity. In this work, four CS-MC-GIC groups with different concentrations were formulated. Group four (CS-MC-GIC-4) gave a significant performance as an anticandidal agent against selected PDR Candida strain, with an obvious decrease in its cell viability and high antibiofilm activity. It also, enhanced all the mechanical properties and supports cell viability of Vero cells as a nontoxic compound. Moreover, CS-MC-GIC-4 inhibited neuraminidases completely, which might provide a novel mechanism to prevent dental/oral infections. Thus, findings in this study open up new prospect of the utilization of CS-MC-GIC as a novel dental filling material against oral drug-resistant Candida.

A novel study on the inhibitory effect of marine macroalgal extracts on hyphal growth and biofilm formation of candidemia isolates

Biofilm formation and hyphal growth are considered to be the most serious virulence factors of Candida species in blood causing candidemia infections, which are difficult to treat due to the spread of resistant Candida isolates to most antifungal drugs. Therefore, in this study, we investigated the effect of different types and concentrations of selected macroalgal extracts from Cladostephus spongiosus (Phaeophyta), Laurencia papillosa (Rhodophyta), and Codium arabicum (Chlorophyta) in inhibiting those virulence factors of the isolated Candida. Acetone extract of C. spongiosus (AECS) showed a stronger anticandidal activity against the selected strains than ethanol extract. Candida krusei was the highest biofilm producer among the selected isolates. AECS showed an inhibition of C. krusei biofilm formation as well as a reduction in the viability of preformed biofilms. Also, AECS reduced various sugars in the candidal exo-polysaccaride layer (EPS). Scanning electron microscopy (SEM) and light microscopic images revealed an absence of hyphae and an alteration in the morphology of biofilm cells when treated with AECS. Moreover, AECS downregulated the expression of hyphal specific genes, hyphal wall protein 1 (HWP1), Agglutinin-like protein 1 (ALS1) and fourth secreted aspartyl proteinase (SAP4), which confirmed the inhibitory effect of AECS on hyphal growth and biofilm formation. Gas chromatography-mass spectrophotometer (GC-MS) analysis of AECS showed three major compounds, which were non-existent in the ethanol extract, and might be responsible for the anticandidal activity; these revealed compounds were 4-hydroxy-4-methyl-2-pentanone, n-hexadecenoic acid, and phenol, 2-methoxy-4-(2-propenyl). These active compounds of AECS may be promising for future pharmaceutical applications in the treatment of candidemia.

Molecular and Histological Association Between Candida albicans from Oral Soft Tissue and Carious Dentine of HIV-Positive Children

Candida albicans and caries are frequently investigated among healthy and immunosuppressed individuals. The objective of this study was to demonstrate the presence of C. albicans on both oral soft and hard tissue and to investigate, at molecular level, the genetic subtype of the organism from the two oral sites. Tongue swabs and dentine scrapings from 362 HIV-positive children, referred for the extraction of carious primary teeth, were cultured on CHROMagar and identified to species level with ID32C. Histological staining of extracted carious teeth was also done. In patients with positive C. albicans cultures from both the tongue and carious dentine, DNA fingerprinting of such paired isolates was performed, using Southern blot hybridisation with the Ca3 probe. Yeasts were cultured from the tongue of 151 (41.7 %) individuals and 57 (37.7 %) simultaneously yielded positive C. albicans cultures from carious dentine. Nine different yeast spp. were identified from the tongue using the ID32C commercial system, but C. albicans was the only species recovered from carious dentine and histological investigation demonstrated fungal elements penetrated into the dentine and not limited to superficial debris on the floor of the cavity. Twelve of 13 paired isolates of C. albicans revealed identical fingerprinting patterns. The findings from this study demonstrated that in a particular individual, the same genetic subtype of C. albicans was capable of colonising both oral soft tissue and carious dentine. This renders carious teeth a constant source, or reservoir, of potentially infectious agents and, particularly among immunosuppressed individuals, should therefore not be left unattended.

Distribution of different yeasts isolates among trauma patients and comparison of accuracy in identification of yeasts by automated method versus conventional methods for better use in low resource countries

INTRODUCTION

As most trauma patients require long-term hospital stay and long-term antibiotic therapy, the risk of fungal infections in such patients is steadily increasing. Early diagnosis and rapid treatment is life saving in such critically ill trauma patients.

AIMS

To see the distribution of various species of Candida among trauma patients and compare the accuracy, rapid identification and cost effectiveness between VITEK 2, CHROMagar and conventional methods.

SETTINGS AND DESIGN

Retrospective laboratory-based surveillance study performed over a period of 52 months (January 2009 to April 2013) at a level I trauma centre in New Delhi, India.

MATERIALS AND METHODS

All microbiological samples positive for Candida were processed for microbial identification using standard methods. Identification of Candida was done using chromogenic medium and by automated VITEK 2 Compact system and later confirmed using the conventional method. Time to identification in both was noted and accuracy compared with conventional method.

STATISTICAL ANALYSIS

Performed using the SPSS software for Windows (SPSS Inc. Chicago, IL, version 15.0). P values calculated using χ2 test for categorical variables. A P<0.05 was considered significant.

RESULTS

Out of 445 yeasts isolates, Candida tropicalis (217, 49%) was the species that was maximally isolated. VITEK 2 was able to correctly identify 354 (79.5%) isolates but could not identify 48 (10.7%) isolates and wrongly identified or showed low discrimination in 43 (9.6%) isolates but CHROM agar correctly identified 381 (85.6%) isolates with 64 (14.4%) misidentification. Highest rate of misidentification was seen in C. tropicalis and C. glabrata (13, 27.1% each) by VITEK 2 and among C. albicans (9, 14%) by CHROMagar.

CONCLUSIONS

Though CHROMagar gives identification at a lower cost compared with VITEK 2 and are more accurate, which is useful in low resource countries, its main drawback is the long duration taken for complete identification.

Are the Conventional Commercial Yeast Identification Methods Still Helpful in the Era of New Clinical Microbiology Diagnostics? A Meta-Analysis of Their Accuracy

Accurate identification of pathogenic species is important for early appropriate patient management, but growing diversity of infectious species/strains makes the identification of clinical yeasts increasingly difficult. Among conventional methods that are commercially available, the API ID32C, AuxaColor, and Vitek 2 systems are currently the most used systems in routine clinical microbiology. We performed a systematic review and meta-analysis to estimate and to compare the accuracy of the three systems, in order to assess whether they are still of value for the species-level identification of medically relevant yeasts. After adopting rigorous selection criteria, we included 26 published studies involving Candida and non-Candida yeasts that were tested with the API ID32C (674 isolates), AuxaColor (1,740 isolates), and Vitek 2 (2,853 isolates) systems. The random-effects pooled identification ratios at the species level were 0.89 (95% confidence interval [CI], 0.80 to 0.95) for the API ID32C system, 0.89 (95% CI, 0.83 to 0.93) for the AuxaColor system, and 0.93 (95% CI, 0.89 to 0.96) for the Vitek 2 system (P for heterogeneity, 0.255). Overall, the accuracy of studies using phenotypic analysis-based comparison methods was comparable to that of studies using molecular analysis-based comparison methods. Subanalysis of studies conducted on Candida yeasts showed that the Vitek 2 system was significantly more accurate (pooled ratio, 0.94 [95% CI, 0.85 to 0.99]) than the API ID32C system (pooled ratio, 0.84 [95% CI, 0.61 to 0.99]) and the AuxaColor system (pooled ratio, 0.76 [95% CI, 0.67 to 0.84]) with respect to uncommon species (P for heterogeneity, <0.05). Subanalysis of studies conducted on non-Candida yeasts (i.e., Cryptococcus, Rhodotorula, Saccharomyces, and Trichosporon) revealed pooled identification accuracies of ≥98% for the Vitek 2, API ID32C (excluding Cryptococcus), and AuxaColor (only Rhodotorula) systems, with significant low or null levels of heterogeneity (P > 0.05). Nonetheless, clinical microbiologists should reconsider the usefulness of these systems, particularly in light of new diagnostic tools such as matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, which allow for considerably shortened turnaround times and/or avoid the requirement for additional tests for species identity confirmation.

Use of the VITEK 2 system to identify and test the antifungal susceptibility of clinically relevant yeast species

Eleven quality control isolates (Candida albicans ATCC 64548, C. tropicalis ATCC 200956, C. glabrata ATCC 90030, C. lusitaniae ATCC 200951, C. parapsilosis ATCC 22019, C. krusei ATCC 6258, C. dubliniensis ATCC 6330, Saccharomyces cerevisiae ATCC 9763, Cryptococcus neoformans ATCC 90012, C. gattii FIOCRUZ-CPF 60, and Trichosporon mucoides ATCC 204094) and 32 bloodstream isolates, including C. albicans, C. tropicalis, C. parapsilosis, C. glabrata, C. krusei, C. guilliermondii, C. pelliculosa (Pichia anomala), C. haemulonii, C. lusitaniae, and C. kefyr were identified at the species level by the VITEK 2 system. A set of clinical isolates (32 total) were used as challenge strains to evaluate the ability of the VITEK 2 system to determine the antifungal susceptibility of yeasts compared with the CLSI and EUCAST BMD reference standards. The VITEK 2 system correctly identified 100% of the challenge strains. The identification of yeast species and the evaluation of their susceptibility profiles were performed in an automated manner by the VITEK 2 system after approximately 15 h of growth for most species of Candida. The VITEK 2 system ensures that each test is performed in a standardized manner and provides quantitative MIC results that are reproducible and accurate when compared with the BMD reference methods. This system was able to determine the MICs of amphotericin B, flucytosine, voriconazole, and fluconazole in 15 h or less for the most common clinically relevant Candida species. In addition, the VITEK 2 system could reliably identify resistance to flucytosine, voriconazole, and fluconazole and exhibits excellent quantitative and qualitative agreement with the CLSI or EUCAST broth microdilution reference methods.

Fungal diagnostics: review of commercially available methods

Fungi and yeasts are critical causes of acute infection. As such, the detection and identification of these organisms are crucial in the diagnosis of affected patient populations. There is a vast array of commercial tests currently available for diagnostic purposes. These vary from traditional culture and biochemical methods to advanced multiparameter molecular tests. Recent technological advances have driven the development of rapid tests which are complementing and in some cases replacing the more traditional methods of detection. Irrespective of the method used the ultimate goal is timely detection of the infectious agent allowing appropriate treatment and improved outcome for the patient.

Rapid identification of yeast isolates from clinical specimens in critically ill trauma ICU patients

Purpose:

The purpose was to evaluate the performance of a commercially available chromogenic Candida speciation media and the Vitek 2 ID system for the identification of medically important yeasts and yeast-like organisms in a routine clinical microbiology laboratory.

Materials and Methods:

A total of 429 non duplicate, consecutive yeast strains were included during the 3.5-year study period. The performance of the Vitek 2 ID system and a chromogenic agar medium was evaluated against the gold standard conventional phenotypic and biochemical identification method for speciation of yeast isolates from trauma patients.

Results:

Candida tropicalis (64%) was the most common Candida species, followed by Candida albicans (14%), Candida rugosa (7%), and Candida parapsilosis (6.5%). Of the 429 isolates, 183 could be identified to species level by all the three methods. Agreement between the chromogenic agar method and conventional methods was 80% for Candida tropicalis, 100% for Candida rugosa, 89% for Candida albicans, and 77% for Candida parapsilosis. Vitek 2 had lower sensitivity, with agreement of 49% for Candida tropicalis, 100% for Candida rugosa, 39% for Candida albicans, and 31% for Candida parapsilosis.

Conclusion:

Thus, in long-term ICU patients, an increasing trend of isolating nonalbicans Candida spp. continues. The chromogenic agar medium is a convenient and economic method to identify commonly isolated species in busy clinical microbiology laboratories.

Identification of yeast isolated from dermatological patients by MALDI-TOF mass spectrometry

Species identification of yeasts is based on biochemical (e.g. API ID 32 C®, bioMérieux) and molecular biological approaches. As an alternative to DNA-dependent methods, mass spectral analysis based identification of micro-organisms has become increasingly recognized. In a number of studies, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been applied for the rapid classification and identification of micro-organisms. In this study, the applicability of MALDI-TOF MS for identifying yeasts isolated from dermatological patients was analysed and compared with the results from the API ID 32 C® system. Furthermore, sequencing the internal transcribed spacer (ITS) regions of the ribosomal DNA was employed as reference method. Candida (C.) albicans was isolated in 41.9% of all cases, C. parapsilosis in 20.3%, C. glabrata in 10.8%, and C. krusei in 6, 8.1%. Rarely isolated yeasts were Candida colliculosa, famata, guilliermondii, lusitaniae, and tropicalis as well as Geotrichum candidum, Rhodotorula mucilaginosa and Trichosporon mucoides. The MALDI TOF results were equal to the results gained by ITS sequence analysis in 94%, whereas API ID 32 C® provided the correct diagnosis in 84.3% (of all cases). This lower identification rate is mostly referable to frequent misidentifications of C. krusei as C. inconspicua/norvegensis,Candida tropicalis, or Geotrichum capitatum. In contrast, all C. krusei strains were correctly identified by MALDI TOF MS. In conclusion, species identification by MALDI-TOF MS was proven to be consistent with ITS sequence analysis; the technique has a resolving power comparatively as high as ITS sequence analysis.

A case of endocarditis caused by the yeast Pichia fabianii with biofilm production and developed in vitro resistance to azoles in the course of antifungal treatment

Pichia fabianii, a yeast rarely causing human infections, was isolated from the blood of a patient with aortic valve endocarditis. The isolates were initially identified biochemically as Candida pelliculosa, but based on direct sequencing of the ITS2 region of rRNA, they were subsequently reidentified as P. fabianii. Antifungal therapy with fluconazole and later with voriconazole led to the development of resistant variants which had high MIC values to both antifungals. Strong biofilm formation by this yeast could also have played a role in the development of its resistance and allowed for its persistence on the infected valve during antifungal therapy. To our knowledge, this is the first published case of endocarditis and the fourth human infection caused by this yeast species.

Yeast identification--past, present, and future methods

The focus of this review is the evolution of biochemical phenotypic yeast identification methods with emphasis on conventional approaches, rapid screening tests, chromogenic agars, comprehensive commercial methods, and the eventual migration to genotypic methods. As systemic yeast infections can be devastating and resistance is common in certain species, accurate identification to the species level is paramount for successful therapy and appropriate patient care.

Pichia farinosa bloodstream infection in a lymphoma patient

We describe a case of Pichia farinosa bloodstream infection in a lymphoma patient. Phenotypic methods failed to identify the isolate, which was identified by sequence-based methods. This case highlights the importance of implementing molecular methods for the identification of rare fungal pathogens.

Multicenter evaluation of the new VITEK 2 advanced colorimetric yeast identification card

The performance of the new VITEK 2 Advanced Colorimetry yeast identification (YST) card for use with the VITEK 2 system (bioMérieux, Inc., Hazelwood, MO) was compared to that of the API 20C AUX (API) system (bioMérieux SA, Marcy-l'Etoile, France) in a multicenter evaluation. A total of 12 quality control, 64 challenge, and 623 clinical yeast isolates were used in the study. Comparisons of species identification, platform reliability, and substrate reproducibility were made between YST and API, with API considered the reference standard. Quality control testing to assess system and substrate reproducibility matched expected results >/=95% of the time. The YST card correctly identified 100% of the challenge strains, which covered the species range of the manufacturer's performance claims. Using clinical isolates, the YST card correctly identified 98.5%, with 1.0% of isolates incorrectly identified and 0.5% unidentified. Among clinical isolates, the YST card generated fewer low-discrimination results (18.9%) than did API (30.0%). The time to identification with YST was 18 h, compared to 48 to 72 h with API. The colorimetric YST card used with the VITEK 2 provides a highly automated, objective yeast identification method with excellent performance and reproducibility. We found this system useful for timely and accurate identification of significant yeast species in the clinical microbiology laboratory.

Biology of the pathogenic yeast Candida glabrata

The yeasts, being favorite eukaryotic microorganisms used in food industry and biotechnologies for production of biomass and various substances, are also used as model organisms in genetic manipulation, molecular and biological research. In this respect, Saccharomyces cerevisiae is the best-known species but current situation in medicine and industry requires the use of other species. Here we summarize the basic taxonomic, morphological, physiological, genetic, etc. information about the pathogenic yeast Candida glabrata that is evolutionarily very closely related to baker's yeast.

Identification of medically important yeast species by sequence analysis of the internal transcribed spacer regions

Infections caused by yeasts have increased in previous decades due primarily to the increasing population of immunocompromised patients. In addition, infections caused by less common species such as Pichia, Rhodotorula, Trichosporon, and Saccharomyces spp. have been widely reported. This study extensively evaluated the feasibility of sequence analysis of the rRNA gene internal transcribed spacer (ITS) regions for the identification of yeasts of clinical relevance. Both the ITS1 and ITS2 regions of 373 strains (86 species), including 299 reference strains and 74 clinical isolates, were amplified by PCR and sequenced. The sequences were compared to reference data available at the GenBank database by using BLAST (basic local alignment search tool) to determine if species identification was possible by ITS sequencing. Since the GenBank database currently lacks ITS sequence entries for some yeasts, the ITS sequences of type (or reference) strains of 15 species were submitted to GenBank to facilitate identification of these species. Strains producing discrepant identifications between the conventional methods and ITS sequence analysis were further analyzed by sequencing of the D1-D2 domain of the large-subunit rRNA gene for species clarification. The rates of correct identification by ITS1 and ITS2 sequence analysis were 96.8% (361/373) and 99.7% (372/373), respectively. Of the 373 strains tested, only 1 strain (Rhodotorula glutinis BCRC 20576) could not be identified by ITS2 sequence analysis. In conclusion, identification of medically important yeasts by ITS sequencing, especially using the ITS2 region, is reliable and can be used as an accurate alternative to conventional identification methods.

Comparison of VITEK 2 with ITS2-fragment length polymorphism analysis for identification of yeast species

A total of 61 clinical yeast isolates of Candida, Cryptococcus, Blastoschizomyces, and Saccharomyces spp. were used to compare two identification techniques, VITEK 2 and ITS2-fragment length polymorphism analysis (ITS2-FLP), with ID32C as the reference method. ID32C identified 58 isolates correctly. ITS2-FLP with Instagene DNA extraction identified 59 isolates. ITS2-FLP combined with boiling-freezing DNA extraction identified 55 isolates. VITEK 2 identified 41 isolates correctly.

Experience with the MicroSeq D2 large-subunit ribosomal DNA sequencing kit for identification of commonly encountered, clinically important yeast species

Experience with a MicroSeq D2 large-subunit (LSU) ribosomal DNA (rDNA) sequencing kit for identification of yeast species commonly encountered in the mycology laboratory at Mayo Clinic is described here. A total of 131 isolates of yeasts recovered from clinical specimens were included in the study. Phenotypic methods used for initial identification included germ tube formation, urease production, microscopic morphological features on cornmeal agar, and an API 20C AUX system; all isolates were sequenced using a MicroSeq D2 LSU rDNA sequencing kit. Nucleic acid sequencing identified 93.9% of the isolates to the correct genus and species. A total of 100 of the isolates (representing 19 species of Candida) were sequenced, and 98% gave results concordant with identifications made by the API 20C AUX system; distance scores ranged from 0 to 1.88%, with an average value of 0.23%. Candida dubliniensis was not included in the MicroSeq database and was identified as Candida albicans. A total of 32 isolates representing 9 other genera (including Cryptococcus, Filobasidium, Kloeckera, Malassezia, Pichia, Sporidiobolus, Rhodotorula, Zygosaccharomyces, and Trichosporon) were included, and 81.3% showed concordant results when phenotypic and sequencing results were compared. Most discrepancies were attributed to the lack of inclusion of the species in the MicroSeq or API 20C AUX database. The MicroSeq D2 LSU rDNA sequencing kit appears to be accurate and useful for the identification of yeasts that might be seen in a clinical laboratory.

Development of a novel, simple and rapid molecular identification system for clinicalCandidaspecies

Identification of clinical yeast isolates causing candidiasis is routinely performed by commercial yeast identification systems based on biochemical, morphological and physiological tests. These systems require 3-5 days and the proportion of identifications that are incorrect is high. Our novel and rapid molecular identification system for clinical Candida species is based on the analysis of restriction patterns obtained from PCR-generated ribosomal DNA sequences using five restriction enzymes. A software package (CandID) was designed to include a database of restriction fragment length polymorphism (RFLP) patterns for 29 Candida species. For 'in-house' validation, 122 clinical isolates that had previously identified in clinical laboratories were typed by this system. These clinical isolates were also independently re-identified by the API 20C AUX system. The ribosomal DNA RFLP database in the context of supporting analytical software allowed simple and rapid (1 work day) identification.

Performance of BacticardTM Candida compared with the germ tube test for the presumptive identification of Candida albicans

Bacticard Candida was compared with the germ tube test for the rapid, presumptive identification of Candida albicans. This test kit detects the enzymatic activities l-proline aminopeptidase and beta-galactosaminidase in yeast colonies grown on culture media. Candida albicans produces both enzymes whereas other yeasts produce only one or neither of the enzymes. We evaluated 536 isolates including eight genera and 33 species of medically important yeasts, including 228 C. albicans and 36 C. dubliniensis. Both tests did not discriminate between C. albicans and C. dubliniensis isolates. The sensitivity and specificity for the Bacticard Candida test were 97.8 and 96.5%, respectively. Bacticard Candida and germ tube tests detected 246 (93.2%), and 256 (97%) C. albicans plus C. dubliniensis isolates. There were eight false-positive results with BactiCard Candida kit and four false-positive results with the germ tube test. Positive and negative predictive values for Bacticard Candida enzymatic test were 95.3 and 98.4%, respectively, while 97.4 and 98.1% for the germ tube test, its specificity being 98.1% and efficiency 97% (97.7% for germ tube). We have observed slightly lower values of sensitivity and specificity than those reported by others using the BactiCard test kit. Bacticard Candida provides a rapid and accurate alternative to the germ tube test for the presumptive identification of C. albicans.

Epidemiology of Candida species infections in critically ill non-immunosuppressed patients

A substantial proportion of patients become colonised with Candida spp during hospital stay, but only few subsequently develop severe infection. Clinical signs of severe infection manifest early but lack specificity until late in the course of the disease, thus representing a particular challenge for diagnosis. Mostly nosocomial, invasive candidiasis occurs in only 1-8% of patients admitted to hospitals, but in around 10% of patients housed in intensive care units where it can represent up to 15% of all nosocomial infections. We review the epidemiology of invasive candidiasis in non-immunocompromised, critically ill patients with special emphasis on disease trends over time, pathophysiology, diagnostic approach, risk factors, and impact. Recent epidemiological data suggesting that the emergence of non-albicans candida strains with reduced susceptibility to azoles, previously linked to the use of new antifungals for empiric and prophylactic therapy in immunocompromised patients, may not have occurred in the critically ill. Management of invasive candidiasis in these patients will be addressed in the December issue of The Lancet Infectious Diseases.

Rapid identification of Candida glabrata with a new commercial test, GLABRATA RTT

The GLABRATA RTT test (Fumouze Diagnostics, Levallois Perret, France) is based on the ability of Candida glabrata to hydrolyze trehalose but not maltose. It requires an inoculum of only four to six colonies, and the results are available within 20 min. We tested GLABRATA RTT with 330 stock isolates grown in subcultures on four different primary fungal isolation media and obtained a sensitivity of 94 to 98% (depending on the medium used) and a specificity of 97.3 to 98.6%. The false-positive results corresponded to C. tropicalis, C. famata, and C. lusitaniae. GLABRATA RTT thus offers rapid and reliable identification of C. glabrata.

Isolation and characterization of a species-specific DNA fragment for identification of Candida (Torulopsis) glabrata by PCR

A PCR specific for Candida glabrata that amplifies a mitochondrial rRNA gene fragment was developed by analysis of C. glabrata-specific agarose gel bands, which were generated by arbitrarily primed PCR. The expected PCR product was successfully amplified with genomic DNA from 95 C. glabrata isolates but not from a number of other fungal isolates.

Evaluation of Candida ID, a new chromogenic medium for fungal isolation and preliminary identification of some yeast species

Candida ID, a new chromogenic medium, allows identification of Candida albicans (blue colonies) and preliminary identification into a group of four species (pink colonies). In comparison with Albicans ID2 and Sabouraud gentamicin chloramphenicol on 446 fungal strains, Candida ID allowed the isolation of more species than Albicans ID 2 (95.5% versus 91.2%).

Yeast identification in the clinical microbiology laboratory: phenotypical methods

Emerging yeast pathogens are favoured by increasing numbers of immunocompromised patients and by certain current medical practices. These yeasts differ in their antifungal drug susceptibilities, and rapid species identification is imperative. A large variety of methods have been developed with the aim of facilitating rapid, accurate yeast identification. Significant recent commercial introductions have included species-specific direct enzymatic colour tests, differential chromogenic isolation plates, direct immunological tests, and enhanced manual and automated biochemical and enzymatic panels. Chromogenic isolation media demonstrate better detection rates of yeasts in mixed cultures than traditional media, and allow the direct identification of Candida albicans by means of colony colour. Comparative evaluation of rapid methods for C. albicans identification, including the germ tube test, shows that chromogenic media may be economically advantageous. Accurate tests for single species include the Bichrolatex Albicans and Krusei Color tests, both immunologically based, as well as the Remel Rapid Trehalose Assimilation Broth for C. glabrata. Among broad-spectrum tests, the RapID Yeast Plus system gives same-day identification of clinical yeasts, but performance depends on inoculum density and geographic isolate source. The API 20 C AUX system is considered a reference method, but newer systems such as Auxacolor and Fungichrom are as accurate and are more convenient. Among automated systems, the ID 32 C strip, the Vitek Yeast Biochemical Card and the Vitek 2 ID-YST system correctly identify >93% of common yeasts, but the ID-YST is the most accurate with uncommon yeasts, including C. dubliniensis. Spectroscopic methods such as Fourier transformed-infrared spectroscopy offer potential advantages for the future. Overall, the advantages of rapid yeast identification methods include relative simplicity and low cost. For all rapid methods, meticulous, standardized multicenter comparisons are needed before tests are fully accepted.

Evaluation of the VITEK 2 system for rapid identification of yeasts and yeast-like organisms

The new VITEK 2 system is a fully automated system dedicated to the identification and susceptibility testing of microorganisms. In conjunction with the VITEK ID-YST card the VITEK 2 system allows the identification of clinically important yeasts and yeast-like organisms in 15 h due to a sensitive fluorescence-based technology. The ID-YST card consists of 47 biochemical reactions. The database comprises 51 taxa, including newly described species. In this study we evaluated the reliability of the VITEK ID-YST card for the identification of yeasts and yeast-like organisms encountered in a clinical microbiology laboratory. A total of 241 strains representing 21 species were studied. The strains were isolated from clinical samples within a period of 60 days prior to the identification. The tests were performed using 24-h to 55-h subcultures on Sabouraud-gentamicin-chloramphenicol agar. Each strain was tested in parallel using the ID 32C strip as a comparison method combined with microscopic morphology and an agglutination test for C. krusei. Overall, 222 strains (92.1%) were unequivocally identified including 11 isolates (4.6%) identified with low discrimination resolved by simple additional tests. Ten strains (4. 1%) for which results were given with low discrimination could not be unequivocally identified with supplemental tests, 4 strains (1. 7%) were misidentified and 5 strains (2.1%) could not be identified. In conclusion, we found that the VITEK 2 system is a rapid and accurate method for the identification of medically important yeasts and yeast-like organisms.

Rapid identification of clinical yeast isolates using the colorimetric AUXACOLOR system

The AUXACOLOR colorimetric system (Sanofi Diagnostics Pasteur, Marnes-la-Coquette, France) for the identification of clinical yeast isolates, was compared in its identification of 100 yeast strains to conventional identification methods. Of the 94 correctly identified isolates, 47% (n = 44) were identified by 24 h, and 100% (n = 94) were identified by 48 h. AUXACOLOR is a simple, rapid and accurate method for the identification of yeast pathogens.

Evaluation of the RapID Yeast Plus System for the identification of yeast

We evaluated the RapID Yeast Plus System using 117 fresh and frozen clinical yeast isolates. The Uni-Yeast-Tek System was used to establish the correct identification. The Vitek System was used as the arbiter for any discrepant results, along with morphology. Of 117 isolates tested, the RapID Yeast Plus System identified 96.6% correctly. The RapID Yeast Plus System is an accurate and reliable alternative to other commonly used yeast identification systems.

Comparative study of seven commercial yeast identification systems

AIMS

To compare the performance of seven commercial yeast identification methods with that of a reference method, and to compare the costs of the commercial kits.

METHODS

Clinical yeast isolates (n = 52), comprising 19 species, were identified using Vitek, Api ID 32C, Api 20C AUX, Yeast Star, Auxacolor, RapID Yeast Plus system, and Api Candida and compared with a reference method which employed conventional tests.

RESULTS

The percentage of correctly identified isolates varied between 59.6% and 80.8%. Overall, the highest performance was obtained with Api Candida (78.8%) and Auxacolor (80.8%). Among germ tube negative yeast isolates, Auxacolor and Api Candida both identified 93.1% of isolates correctly. All systems failed to identify C norvegensis, C catenulata, C haemulonii, and C dubliniensis. In comparison with Auxacolor, the Api Candida is less expensive and requires less bench time.

CONCLUSIONS

Auxacolor and Api Candida appeared to be the most useful systems for identification of germ tube negative yeast isolates in clinical microbiology laboratories, although one should be aware that several germ tube negative Candida species cannot be identified by these systems.

Comparison of the API Candida system with the AUXACOLOR system for identification of common yeast pathogens

Two commercial systems for the identification of yeasts were evaluated by using 159 clinical isolates that had also been identified by conventional biochemical and morphological methods. The API Candida system correctly identified 146 isolates (91.8%), and the AUXACOLOR system correctly identified 145 isolates (91.2%). However, of the 146 isolates identified by the API Candida system, 23 required supplemental biochemical tests or morphological assessment to obtain the correct identification. The AUXACOLOR system gave no identification in 13 cases (8.2%), while the API Candida system gave an unreadable profile in only one case. Incorrect identifications were more common with the API Candida system (12 isolates; 7.5%) than with the AUXACOLOR system (1 isolate; 0.6%).