Evaluation of the MicroScan Rapid Yeast Identification panel

Kombucha: Production and Microbiological Research

Kombucha is a sparkling sugared tea commonly prepared using a sugared tea infusion and fermented at ambient temperature for several days using a cellulose pellicle also called tea fungus that is comprised of acetic acid bacteria and yeast. Consumption of Kombucha has been reported as early as 220 B.C. with various reported potential health benefits and appealing sensory properties. During Kombucha fermentation, sucrose is hydrolysed by yeast cells into fructose and glucose, which are then metabolised to ethanol. The ethanol is then oxidised by acetic acid bacteria (AAB) to produce acetic acid which is responsible for the reduction of the pH and also contributes to the sour taste of Kombucha. Characterisation of the AAB and yeast in the Kombucha starter culture can provide a better understanding of the fermentation process. This knowledge can potentially aid in the production of higher quality products as these microorganisms affect the production of metabolites such as organic acids which are associated with potential health benefits, as well as sensory properties. This review presents recent advances in the isolation, enumeration, biochemical characteristics, conventional phenotypic identification system, and modern genetic identification techniques of AAB and yeast present in Kombucha to gain a better understanding of the microbial diversity of the beverage.

Comparison between MALDI-TOF MS and MicroScan in the identification of emerging and multidrug resistant yeasts in a fourth-level hospital in Bogotá, Colombia

Background

The introduction of MALDI-TOF MS in the clinical microbiology laboratory has modified the approaches for the identification of fungi. Thanks to this tool, it is possible to identify cryptic species, which possess critical susceptibility patterns. Clinical strains were identified using the MicroScan and MALDI-TOF MS systems. Discrepant results from both methods were investigated using ITS rDNA barcoding. Finally, these isolates were also tested for in vitro susceptibility.

Results

The percentage of agreement between both methods to 498 yeast isolates was of 93.6% (32 discrepant isolates). The concordance of ITS sequencing with MALDI-TOF MS was higher (99%) than that of MicroScan (94%). Several of these discordant yeasts displayed high MICs for antifungal agents.

Conclusions

Our study highlights the need of the MS and molecular approaches such as MALDI-TOF MS and ITS rDNA barcoding for the correct identification of emerging or cryptic yeast species; besides, some of these could be multidrug resistant.

This work was the first experience in the implementation of the MALDI-TOF MS technology in Colombia. We found the first uncommon yeasts including Candida auris and we could identify Trichosporon faecalis. Our work highlights a clear necessity of an accurate yeast identification as a much more pertinent technique than the susceptibility profiles, because the most unusual yeasts exhibit resistance profiles to the few available antifungals.

[Recommendations for the diagnosis of candidemia in Latin America. Grupo Proyecto Épico]

Candidemia is one of the most frequent opportunistic mycoses worldwide. Limited epidemiological studies in Latin America indicate that incidence rates are higher in this region than in the Northern Hemisphere. Diagnosis is often made late in the infection, affecting the initiation of antifungal therapy. A more scientific approach, based on specific parameters, for diagnosis and management of candidemia in Latin America is warranted. 'Recommendations for the diagnosis and management of candidemia' are a series of manuscripts that have been developed by members of the Latin America Invasive Mycosis Network. They aim to provide a set of best-evidence recommendations for the diagnosis and management of candidemia. This publication, 'Recommendations for the diagnosis of candidemia in Latin America', was written to provide guidance to healthcare professionals on the diagnosis of candidemia, as well as on the usefulness and application of susceptibility testing in patients who have a confirmed diagnosis of candidemia. Computerized searches of existing literature were performed by PubMed. The data were extensively reviewed and analyzed by members of the group. The group also met on two occasions to pose questions, discuss conflicting views, and deliberate on a series of management recommendations. 'Recommendations for the diagnosis of candidemia in Latin America' includes diagnostic methods used to detect candidemia, Candida species identification, and susceptibility testing. The availability of methods, their costs and treatment settings are considered. This manuscript is the first of this series that deals with diagnosis and treatment of invasive candidiasis. Other publications in this series include: 'Recommendations for the management of candidemia in adults in Latin America', 'Recommendations for the management of candidemia in children in Latin America', and 'Recommendations for the management of candidemia in neonates in Latin America'.

Recommendations for the diagnosis of candidemia in Latin America. Latin America Invasive Mycosis Network

Candidemia is one of the most frequent opportunistic mycoses worldwide. Limited epidemiological studies in Latin America indicate that incidence rates are higher in this region than in the Northern Hemisphere. Diagnosis is often made late in the infection, affecting the initiation of antifungal therapy. A more scientific approach, based on specific parameters, for diagnosis and management of candidemia in Latin America is warranted. 'Recommendations for the diagnosis and management of candidemia' are a series of manuscripts that have been developed by members of the Latin America Invasive Mycosis Network. They aim to provide a set of best-evidence recommendations for the diagnosis and management of candidemia. This publication, 'Recommendations for the diagnosis of candidemia in Latin America', was written to provide guidance to healthcare professionals on the diagnosis of candidemia, as well as on the usefulness and application of susceptibility testing in patients who have a confirmed diagnosis of candidemia. Computerized searches of existing literature were performed by PubMed. The data were extensively reviewed and analyzed by members of the group. The group also met on two occasions to pose questions, discuss conflicting views, and deliberate on a series of management recommendations. 'Recommendations for the diagnosis of candidemia in Latin America' includes diagnostic methods used to detect candidemia, Candida species identification, and susceptibility testing. The availability of methods, their costs and treatment settings are considered. This manuscript is the first of this series that deals with diagnosis and treatment of invasive candidiasis. Other publications in this series include: 'Recommendations for the management of candidemia in adults in Latin America', 'Recommendations for the management of candidemia in children in Latin America', and 'Recommendations for the management of candidemia in neonates in Latin America'.

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.

Current knowledge of Trichosporon spp. and Trichosporonosis

Trichosporon spp. are basidiomycetous yeast-like fungi found widely in nature. Clinical isolates are generally related to superficial infections. However, this fungus has been recognized as an opportunistic agent of invasive infections, mostly in cancer patients and those exposed to invasive medical procedures. It is possible that the ability of Trichosporon strains to form biofilms on implanted devices, the presence of glucuronoxylomannan in their cell walls, and the ability to produce proteases and lipases are all factors likely related to the virulence of this genus and therefore may account for the progress of invasive trichosporonosis. Disseminated trichosporonosis has been increasingly reported worldwide and represents a challenge for both diagnosis and species identification. Phenotypic identification methods are useful for Trichosporon sp. screening, but only molecular methods, such as IGS region sequencing, allow the complete identification of Trichosporon isolates at the species level. Methods for the diagnosis of invasive trichosporonosis include PCR-based methods, Luminex xMAP technology, and, more recently, proteomics. Treating patients with trichosporonosis remains a challenge because of limited data on the in vitro and in vivo activities of antifungal drugs against clinically relevant species of the genus. Despite the mentioned limitations, the use of antifungal regimens containing triazoles appears to be the best therapeutic approach.

Enzymatic substrates in microbiology

Enzymatic substrates are powerful tools in biochemistry. They are widely used in microbiology to study metabolic pathways, to monitor metabolism and to detect, enumerate and identify microorganisms. Synthetic enzymatic substrates have been customized for various microbial assays, to detect an expanding range of both new enzymatic activities and target microorganisms. Recent developments in synthetic enzymatic substrates with new spectral, chemical and biochemical properties allow improved detection, enumeration and identification of food-borne microorganisms, clinical pathogens and multi-resistant bacteria in various sample types. In the past 20 years, the range of synthetic enzymatic substrates used in microbiology has been markedly extended supporting the development of new multi-test systems (e.g., Microscan, Vitek 2, Phoenix) and chromogenic culture media. The use of such substrates enables an improvement in time to detection and specificity over conventional tests that employ natural substrates. In the era of intense developments in molecular biology, phenotypic tests involving enzymatic substrates remain useful to analyse both simple and complex samples. Such tests are applicable to diagnostic and research laboratories all over the world.

Applications of a microplate reader in yeast physiology research

Microplate readers have been useful assistants of researchers for several decades. This work is focused on the applications of a simple absorbance microplate reader in yeast physiology research, and its advantages and limitations in comparison with alternative methods are discussed. The two main procedures involved are measuring growth curves and monitoring the pH changes of medium using two different pH indicators. We suggest mathematical formulas for converting absorbance data into pH values. With a microplate reader, as many as 96 samples can be simultaneously analyzed, while medium consumption is minimized to 100 µL per sample. The results can be observed in 24–48 h (for growth curves) or in 1–3 h (for pH changes) with minimal hands-on time required.

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.

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.

Cryptococcosis

Cryptococcus neoformans has risen to a worldwide highly recognizable major opportunistic pathogen with deadly consequences. It has become a model fungus to study a variety of paradigms in the host-fungus relationships. Genomic studies are advancing knowledge on its evolution and dissecting its virulence composite. Studies designed to understand host immunology to this fungus are leading to development of active and passive prevention and therapeutic strategies. This article collates and analyzes both new and old knowledge about the pathogen to help frame the meaning of human cryptococcosis as it starts to evolve in the new millennium.

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.

Isolation and identification of Candida from the oral cavity

A number of methods of sampling the oral cavity for the presence of candida have been developed. Such techniques play an important role in the diagnosis and management of oral candidosis. In the past, identification of candida isolated from the oral cavity has usually been limited to the genus Candida or to the species C. albicans. However, with the recognition that Candida species differ in the production of putative virulence factors and sensitivity to antifungal agents, greater emphasis has been placed on identification of isolates to species level. As a result a range of commercially available systems for yeast identification can now be used in conjunction with traditional identification procedures.

Comparative performance of the RapID Yeast Plus System and the API 20C AUX Clinical Yeast System

The performance of the RapID Yeast Plus System (Innovative Diagnostic Systems, Norcross, Ga.), a 4-h micropanel using single-substrate enzymatic test reactions, was compared with that of the API 20C AUX Clinical Yeast System (bioMerieux Vitek, Hazelwood, Mo.), a 48- to 72-h carbohydrate assimilation panel. Two hundred twenty-five yeasts, yeast-like fungi, and algae, comprising 28 species and including 30 isolates of Cryptococcus neoformans, an important pathogen not tested in appreciable numbers in other comparisons, were tested by both methods. On initial testing, 196 (87.1%) and 215 (95.6%) isolates were correctly identified by the RapID and API systems, respectively. Upon repeat testing, the number of correctly identified isolates increased to 220 (97.8%) for the RapID system and 223 (99.1%) for the API system. Reducing the turbidity of the test inoculum to that of a no. 3 McFarland turbidity standard, which is below that recommended by the manufacturer, resulted in the correct identification of most of the isolates initially misidentified by the RapID system, including 10 of 30 C. neoformans isolates. Concordance between the RapID and API results after repeat testing was 97.3%.

Simple strategy for direct identification of medically important yeast species from positive blood culture vials

We compared direct inoculation of the Auxacolor yeast identification system from positive blood culture vials to standard identification with the API 20C AUX (API 20C), using 44 prospectively collected clinical specimens and 25 seeded blood culture vials. Direct inoculation of the Auxacolor system was accurate and more rapid than standard identification with the API 20C.

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%).

Evaluation of the auxacolor system for biochemical identification of medically important yeasts

We compared the Auxacolor yeast identification system (Sanofi Diagnostics Pasteur) with the API 20C Aux (bioMerieux-Vitek) using 105 isolates of medically important yeasts. The Auxacolor system provided more rapid, accurate results and displayed less interobserver variability than the API 20C Aux.

Efficacy of API 20C and ID 32C systems for identification of common and rare clinical yeast isolates

The abilities of the API 20C and ID 32C yeast identification systems to identify 123 common and 120 rare clinical yeast isolates were compared. API 20C facilitated correct identification of 97% common and 88% rare isolates while ID 32C facilitated correct identification of 92% common and 85% rare isolates.

Rapid identification of Candida albicans and other human pathogenic yeasts by using short oligonucleotides in a PCR

A PCR system that can quickly and accurately identify 14 species of human pathogenic yeasts was developed. The procedure distinguished between nine species of a closely related clade, Lodderomyces elongisporus, Candida parapsilosis, a new Candida sp., C. sojae, C. tropicalis, C. maltosa, C. viswanathii, C. albicans, and C. dubliniensis and between another five more divergent species, Pichia guilliermondii, C. glabrata, C. zeylanoides, C. haemulonii, and C. haemulonii type II. A rapid DNA extraction procedure that yields purified DNA in about 1 h is also described. The system uses uniform conditions with four primers for each reaction, two 40- to 50-mer universal primers that serve as a positive control and two 23- to 30-mer species-specific primers. Species-specific primers were derived from a 600-nucleotide variable region (D1/D2) at the 5' end of the large-subunit (26S) ribosomal DNA gene and were generally designed to use mismatches at the 3' end. Universal primers were developed from conserved nucleotide sequences in the small-subunit (18S) rRNA gene. In this system, a control 1,200- to 1,300-base DNA fragment was produced in all reactions and a smaller 114- to 336-base DNA fragment was produced if the chromosomal DNA from the target species was present. The PCR procedure is rapid and easy to interpret and may be used with mixed cultures.

Comparison of RapID yeast plus system with API 20C system for identification of common, new, and emerging yeast pathogens

The ability to identify yeast isolates by the new enzymatic RapID Yeast Plus System was compared to the ability to identify yeast isolates by the API 20C system. A total of 447 yeast isolates representing Blastoschizomyces capitatus, 17 Candida spp., 5 Cryptococcus spp., Geotrichum spp., 2 Hanseniaspora spp., Hansenula anomala, Hansenula wingei, 3 Rhodotorula spp., Saccharomyces cerevisiae, Sporobolomyces salmonicolor, Trichosporon beigelii, and 2 Prototheca spp. were evaluated. Also, five quality control strains (Candida spp. and Cryptococcus laurentii) with well-documented reactivities by the RapID Yeast Plus System were used. Each isolate was evaluated by both methods with a 48-h culture grown at 30 degrees C on Sabouraud dextrose agar (Emmons modification) by following the recommendations of the manufacturers. The RapID Yeast Plus System enzymatic reactions were read after 4 h of incubation, and the API 20C carbohydrate assimilation identification profiles were obtained after 72 h of incubation. There was good (95.7%) agreement between the identifications obtained by the two methods with the eight common Candida spp. and with Cryptococcus neoformans. The agreement was lower when the emerging Candida spp. and other yeast-like pathogens were tested (79.1 and 75.2%, respectively). These preliminary data suggest the potential utility of the RapID Yeast Plus System for use in the clinical laboratory for the rapid identification of common yeast pathogens as well as certain new and emerging species.

Comparison of use of phenotypic and genotypic characteristics for identification of species of the anamorph genus Candida and related teleomorph yeast species

A total of 49 type and neotype isolates and 32 clinical isolates of the anamorph genus Candida and related teleomorph genera were obtained from different culture collections and clinical laboratories. Isolates were subjected to two phenotypic methods of identification, Vitek yeast biochemical card (YBC) and API ID 32C, both based on carbohydrate assimilation, and one genotypic method, PCR fingerprinting, based on the detection of DNA polymorphisms between minisatellite-specific sequences with the primer M13 (5' GAGGGTGGCGGTTCT 3'). The correct identification of a strain at the Centraalbureau voor Schimmelcultures was used as the gold standard for the identification of an isolate. When the study was restricted to species included in the respective biochemical databases, the Vitek YBC and API ID 32C systems performed adequately with positive identification rates of 87.3 and 76.8%, respectively. When uncommon species were added to the study, several of which are not included in the databases, the identification efficiencies were 76.5 and 77.5%, respectively. By comparison, all isolates were correctly identified by PCR fingerprinting, with 63 reference species profiles in the databank. Sufficient polymorphisms among the total set of banding patterns were observed, with adequate similarity in the major patterns obtained from a given species, to allow each isolate to be assigned unambiguously to a particular species. In addition, variations in minor bands allowed for differentiation to the strain level. PCR fingerprinting was found to be rapid, reproducible, and more cost-effective than either biochemical approach. Our results provide reference laboratories with an improved identification method for yeasts based on genotypic rather than phenotypic markers.

Ability of RapID Yeast Plus System to identify 304 clinically significant yeasts within 5 hours

The RapID Yeast Plus System (Innovative Diagnostic Systems, Norcross, Ga.) is a qualitative micromethod that uses conventional and chromogenic substrates for the identification of medically important yeasts. The ability of the RapID Yeast Plus system to accurately identify 304 clinical yeast isolates within 5 h was evaluated. The RapID Yeast Plus method correctly identified 286 (94.1%) of strains to the species level without the need for additional tests. A further 12 strains (3.9%) were classified as correct to the genus level or to a low-probability identification with two or more possibilities. In these latter cases, additional tests were required to delineate the correct identification. Organisms in the latter group comprised Candida parapsilosis (n = 1), Candida tropicalis (n = 1), Candida ciferrii (n = 1), Candida guilliermondii (n = 2), Candida humicola (n = 1), Candida kefyr (n = 1), Cryptococcus neoformans (n = 1), and Rhodotorula rubra (n = 4). Six strains (2.0%) were misidentified or did not yield codes in the manufacturer's database. These included one Candida utilis (identified as Candida famata/Candida guilliermondii), one Trichosporon beigelii (identified as Cryptococcus neoformans), one Candida diddensiae (identified as Candida albicans), one Candida membranaefaciens (identified as Candida parapsilosis), one Candida norvegensis (identified as Candida zeylanoides), and one Candida catenulata (no code) isolate; the last four strains are not included in the firm's current database. The RapID Yeast Plus system yielded excellent results and may be recommended for use in the routine laboratory for accurate same-day identification of clinically significant yeasts.

Cryptococcosis in the era of AIDS--100 years after the discovery of Cryptococcus neoformans

Although Cryptococcus neoformans and cryptococcosis have existed for several millennia, a century has passed since the discovery of this encapsulated yeast and its devastating disease. With the advent of the AIDS pandemic, cryptococcal meningitis has emerged as a leading cause of infectious morbidity and mortality and a frequently life-threatening opportunistic mycosis among patients with AIDS. Both basic and clinical research have accelerated in the 1990s, and this review attempts to highlight some of these advances. The discussion covers recent findings, current concepts, controversies, and unresolved issues related to the ecology and genetics of C. neoformans; the surface structure of the yeast; and the mechanisms of host defense. Regarding cell-mediated immunity, CD4+ T cells are crucial for successful resistance, but CD8+ T cells may also participate significantly in the cytokine-mediated activation of anticryptococcal effector cells. In addition to cell-mediated immunity, monoclonal antibodies to the major capsular polysaccharide, the glucuronoxylomannan, offer some protection in murine models of cryptococcosis. Clinical concepts are presented that relate to the distinctive features of cryptococcosis in patients with AIDS and the diagnosis, treatment, and prevention of cryptococcosis in AIDS patients.

Evaluation of the MicroScan enzyme-based system for the identification of foodborne yeasts

Eighty-nine strains representing 36 species of foodborne yeasts isolated from fruit juice concentrates were identified using the Baxter MicroScan enzyme-based kit, conventional tests according to a simplified identification method (SIM), and the API 20C kit. Of the 15 test species included in the MicroScan database, only 40% were correctly identified; 13% gave scores of unacceptably low probabilities, 20% were misidentified, and 27% could not be identified. Of the 21 test species not in the MicroScan database, 38% were misidentified and 62% produced biocodes with between-species differences not larger than differences between strains within species. The reliability of the MicroScan enzyme-based system is questioned, in that different results were sometimes obtained upon retesting the same strains. The MicroScan enzyme-based system is rapid, providing results within 4 h. However, because of its restricted and specific database and unreliability, the system appears to be unsuited for the identification of foodborne yeasts.

Evaluation of the AUXACOLOR system, a new method of clinical yeast identification

AIMS

To compare the AUXACOLOR yeast identification system with the API 20C system.

METHODS

Yeast isolates (n = 215), comprising 16 species, were identified using the AUXACOLOR system and the API 20C system. Isolates that could not be identified with the API 20C system or which produced discrepant results in the two systems were identified by assimilation and fermentation procedures.

RESULTS

AUXACOLOR correctly identified 150 (85.7%) of 175 germ tube negative isolates while API 20C identified 155 (88.6%). Incorrect identifications were more common with API 20C (7.4%) than with AUXACOLOR (3.7%). Of 110 isolates of four common pathogens (Candida glabrata, C parapsilosis, C tropicalis, and Cryptococcus neoformans), 82.7% (91/110) were identified by AUXACOLOR while API 20C identified 74.5% (82/110). Of 65 less common germ tube negative isolates, 55.4% (36/65) were identified by AUXACOLOR while API 20C identified 63.1% (41/65).

CONCLUSION

Although it has a limited database of 26 species, the AUXACOLOR system is a useful method for identification of germ tube negative clinical yeast isolates. Compared with the API 20C, the AUXACOLOR system is simpler and quicker to set up, easier to interpret, and comparable in cost.

RAPD analysis: a rapid technique for differentiation of spoilage yeasts

Techniques for the identification of the spoilage yeasts Saccharomyces cerevisiae and members of the Zygosaccharomyces genus from food and beverages sources were evaluated. The use of identification systems based on physiological characteristics resulted often in incomplete identification or misidentification. Also the cellular fatty acid analysis failed on differentiating species within the Zygosaccharomyces genus. However, the Random Amplified Polymorphic DNA (RAPD) assay, using selected 10-mer oligonucleotides, allowed discrimination between all species tested. For this RAPD assay, a simple and reproducible method of DNA isolation from spoilage yeast cells is described.

Fluconazole, itraconazole and ketoconazole in vitro activity against Candida spp

The in vitro activity of fluconazole, itraconazole and ketoconazole against 625 Candida yeast strains from patients treated at the University Hospital of the Canaries, by means of a micromethod of dilution in broth enriched with Yeast Nitrogen Base (YNB), and buffered to pH7, has been assessed. Species distribution was as follows: Candida albicans (388), Candida tropicalis (84), Candida glabrata (84), Candida parapsilosis (69). Our results show 10.0% and 8.8% of C. albicans resistant to itraconazole and fluconazole, respectively, and 1.8% resistant to ketoconazole; 39.5% of C. tropicalis were resistant to itraconazole, 34.5% to fluconazole and 2.4% to ketaconazole. 19.1% of C. glabrata were resistant to fluconazole and 13.1% to itraconazole; 4.4% of C. parapsilosis were resistant to fluconazole and 1.5% to itraconazole. In general C. tropicalis was the most resistant strain and C. parapsilosis the most sensitive. The greatest percentages of resistance in vitro were seen with the two triazols.

In vitro susceptibility of 545 isolates of Candida spp. to four antifungal agents

The in vitro susceptibility to amphotericin B, fluconazole, itraconazole and ketoconazole of 545 Candida strains from patients treated at the University Hospital of the Canaries was determined by means of a microdilution test. The distribution of the species was as follows: Candida albicans (342), Candida tropicalis (70), Candida glabrata (68), Candida parapsilosis (65). Of Candida albicans isolates, 8.5% and 7.6% showed resistance to itraconazole and fluconazole respectively. Of C. tropicalis isolates 34.3%, 27.1% and 2.9% were resistant to itraconazole, fluconazole and ketaconazole respectively. For C. glabrata, 10.3% and 4.4% of the isolates under study demonstrated resistance to fluconazole and itraconazole respectively. Only 4.6% and 1.5% of C. parapsilosis isolates demonstrated resistance to fluconazole and itraconazole respectively. C. tropicalis was the most resistant strain and C. parapsilosis the most sensitive. The greatest percentages of resistance in vitro were seen with the triazoles.

Evaluation of two commercialized systems for the rapid identification of medically important yeasts

A total of 77 recent clinical isolates of Candida albicans and other medically important yeasts were identified by two different commercial tests, Rapidec albicans (API-bioMérieux) and Fongiscreen 4H (Sanofi Diagnostics Pasteur), and conventional mycological methods. The strains were from 13 different species of yeasts and consisted of strains of 36 C. albicans, three of Candida famata, nine of Candida (Torulopsis) glabrata, five of Candida guilliermondii, two of Candida kefyr, three of Candida krusei, one of Candida lusitaniae, four of Cryptococcus neoformans, five of Candida parapsilosis, six of Candida tropicalis, one of Candida viswanathii, one of Rhodotorula rubra and one of Saccharomyces cerevisiae. According to the reactivity profiles of the isolates, identification was always correct with Fongiscreen 4H and was correct in 97.3% of the strains with Rapidec albicans. The latter test did not identify two C. albicans isolates that were correctly identified by Fongiscreen 4H. Both methods (97.3% correlation) were very useful for identification of C. albicans achieving the aim of their manufacturers. Additionally, Fongiscreen 4H was very useful for the identification of three other species of yeasts: C. glabrata, C. tropicalis and Cr. neoformans. The results of our study indicate that the accuracy of Rapidec albicans and Fongiscreen 4H is similar to that of the conventional methods used in this study for the identification of C. albicans. The same is true of Fongiscreen 4H in the identification of C. glabrata, C. tropicalis and Cr. neoformans. Both tests could be rapid and easy-to-perform tools in the clinical microbiology laboratory, but differences in cost must be taken into account.

Simplified techniques for identifying foodborne yeasts

Four problematic areas associated with the identification of foodborne yeasts are discussed. These consist of (1) the inability of conventional identification tests to recognize some common and important foodborne yeasts characterized by genomic differences (e.g., Saccharomyces cerevisiae, S. bayanus and S. pastorianus); (2) the delay in application of non-traditional identification methods such as DNA fingerprinting, chromosome karyotyping, protein electrophoretic patterns and fatty acid profiles for routine identification purposes; (3) the lack of commercially available manual or automated identification systems dedicated to the diagnosis of foodborne yeasts; and (4) the disregard for considering ecological frequency of yeasts in computerized probabilistic identification systems.

Automated systems for identification of microorganisms

Automated instruments for the identification of microorganisms were introduced into clinical microbiology laboratories in the 1970s. During the past two decades, the capabilities and performance characteristics of automated identification systems have steadily progressed and improved. This article explores the development of the various automated identification systems available in the United States and reviews their performance for identification of microorganisms. Observations regarding deficiencies and suggested improvements for these systems are provided.