Assessment of accuracy of identification of pathogenic yeasts in microbiology laboratories in the United kingdom.

Rapid, accurate identification of yeast isolates from clinical samples has always been important given their innately variable antifungal susceptibility profiles. Recently, this has become paramount with the proposed introduction of species-specific interpretive breakpoints for MICs obtained in yeast antifungal susceptibility tests (M. A. Pfaller, D. Andes, D. J. Diekema, A. Espinel-Ingroff, D. Sheehan, and CLSI Subcommittee for Antifungal Susceptibility Testing, Drug Resist. Updat. 13:180-195, 2010). Here, we present the results of a 12-month evaluation of the accuracy of identifications that accompany yeast isolates submitted to the Mycology Reference Laboratory (United Kingdom) for either confirmation of identity or susceptibility testing. In total, 1,781 yeast isolates were analyzed, and the robustness of prior identifications obtained in microbiology laboratories throughout the United Kingdom was assessed using a combination of culture on chromogenic agar, morphology on cornmeal agar, and molecular identification by pyrosequencing. Over 40% of isolates (755) were submitted without any suggested identification. Of those isolates with a prior identification, 100 (9.7%) were incorrectly identified. Error rates ranged from 5.2% (for organisms submitted for antifungal susceptibility testing) to 18.2% (for organisms requiring confirmation of identity) and varied in a strictly species-specific manner. At least 50% of identification errors would be likely to affect interpretation of MIC data, with a possible impact on patient management. In addition, 2.3% of submitted cultures were found to contain mixtures of at least two yeast species. The vast majority of mixtures had gone undetected in the referring laboratory and would have impacted the interpretation of antifungal susceptibility profiles and patient management. Some of the more common misidentifications are discussed according to the identification method employed, with suggestions for avoiding such misinterpretations.

Evaluación de la calidad del diagnóstico micológico: cultivos / Quality assessment of the mycological diagnosis: cultures

Se evaluó la capacidad de los laboratorios participantes del Sub Programa Micología para identificar diferentes cepas de hongos al nivel de género o especie. Tomados los resultados en conjunto, el 66% de los laboratorios identificó en forma correcta las cepas, mientras que otro 25% lo hizo en forma parcial. En el caso de los dermatofitos hubo un mayor porcentaje de respuestas correctas para el reconocimiento de Trichophyton mentagrophytes (76%) respecto de las especies de Microsporum evaluadas: M. canis (66%) y M. gypseum (65%). Los resultados de la identificación de las especies de levaduras mostraron dos grupos diferentes: uno conformado por Candida albicans y Cryptococcus neoformans, con elevados porcentajes de respuestas correctas (87 y 95%, respectivamente) y otro por C. tropicalis y C. glabrata, que ocasionó dificultades para su correcta identificación (sólo 28 y 32% de respuestas correctas). Las especies de Aspergillus evaluadas (A. fumigatus y A. niger) fueron reconocidas en forma correcta por el 63 y 72% de los participantes. Los resultados obtenidos, si bien son considerados como aceptables, evidencian la necesidad de mejorar la capacidad evaluada, teniendo en cuenta su influencia decisiva sobre la calidad del diagnóstico micológico.

The ability to identify different fungal strains at genera or specie level for participant laboratories of the Mycology Sub-Program, was evaluated. Taking into account all results as a whole, 66% of laboratories identified the strains correctly, while another 25% recognized the strains partially. Regarding dermatophytes, a higher percentage of correct responses for Trichophyton mentagrophytes recognition was observed with respect to (76%) those of the evaluated Microsporum species: M. canis (66%) and M. gypseum (65%). The results produced by the identification of yeasts species showed 2 different groups: one constituted by Candida albicans and Cryptococcus neoformans, with higher percentages of correct responses (87 and 95%, respectively) and another one constituted by C. tropicalis and C. glabrata, which presented difficulties for their correct identification (28 and 32% correct responses). The evaluated species of Aspergillus (A. fumigatus and A. niger) were recognized by 63% and 72% of the participants. The results obtained, considered as acceptable, show the need to improve the evaluated capacity, taking into account their decisive influence on mycologic diagnosis quality.

Comparison of updated Vitek Yeast Biochemical Card and API 20C yeast identification systems.

The updated Vitek Yeast Biochemical Card (YBC) was compared with the API 20C by using 409 germ tube-negative yeasts and Geotrichum spp. that were either clinical or proficiency sample isolates. The API 20C was the reference standard. The 409 isolates represented nine genera and 21 species. Morphology agars were inoculated and interpreted for each isolate. The API 20C identified 406 isolates (99.3%), while the Vitek YBC identified 367 (89.7%). Both systems identified the majority of yeasts after 24 h of incubation--73.4% were identified by the API 20C and 77.4% were identified by the Vitek YBC. The Vitek 24-h reading had some incorrect identifications. These included 14 isolates of Candida tropicalis that were identified as Candida parapsilosis (91 to 97% reliability) and 3 isolates of Candida krusei that were called Blastoschizomyces capitatus (Geotrichum capitatum), Candida rugosa, and Candida zeylanoides. In total, the Vitek YBC misidentified 30 isolates, while the API 20C misidentified 3 isolates. In addition, results for 14 isolates with the Vitek YBC were listed under the category "no identification." Morphology agars were required for identification with 89 isolates (21.9%) when the API 20C was used and with 50 isolates (12.6%) when the Vitek YBC was used. Apart from the price of the Vitek instrument, the API 20C costs $1.28 more per test than the Vitek YBC. Overall, the updated Vitek YBC compares favorably with the API 20C in the identification of common yeasts such as Torulopsis glabrata, C. parapsilosis, and Cryptococcus neoformans. However, problems were encountered with the Vitek system in the identification of C. tropicalis, C. krusei, Trichosporon spp., and some Cryptococcus spp. The routine use of morphology agars with either method is recommended.

Mycology quality assessment: United Kingdom national scheme.

A mycology quality assessment scheme introduced in 1986 was assessed: 289 laboratories participated in the scheme, and six distributions, each containing four specimens, were made. Levels of performance varied considerably among participating laboratories: performance was highest with the commoner organisms distributed, but some laboratories, encouragingly, achieved a consistently high level of species identification. A questionnaire distributed to participants showed that a wide range of methods are commonly used, some of which are contrary to good practice. As the scheme continues, selection of organisms considered to be relevant and of use to participants will become difficult.