Candida dubliniensis and Candida albicans differentiation by colony morphotype in Sabouraud-triphenyltetrazolium agar / Discriminación entre Candida dubliniensis y Candida albicans evaluando el morfotipo de las colonias en agar Sabouraud-trifeniltetrazolio

Background: Candida dubliniensis is a germ tube and chlamydoconidia producing Candida species that may be misidentified as Candida albicans. Molecular-based methods are the most reliable techniques for C. albicans and C. dubliniensis differentiation. However, accurate, quick and inexpensive phenotypic tests are needed to be used in low-complexity mycology laboratories. Aims: To evaluate colony morphotypes on Sabouraud-triphenyltetrazolium agar as a tool for C. dubliniensis and C. albicans differentiation. Methods: The morphology of 126 C. albicans and C. dubliniensis strains was evaluated and compared with their identification by molecular methods. Results: The method showed 100% sensitivity and specificity when color and the presence or absence of large white mycelial halo was evaluated. Conclusions: Colony morphotype on Sabouraud-triphenyltetrazolium agar should be considered as a new tool to differentiate C. dubliniensis and C. albicans (AU)

Antecedentes: Candida dubliniensis es una especie del género Candida capaz de producir tubos germinativos y clamidoconidios, y puede ser identificada erróneamente como Candida albicans. Las técnicas moleculares de identificación son consideradas las más específicas para diferenciar estas especies. Sin embargo, se siguen necesitando métodos exactos, rápidos y de bajo coste para ser utilizados en laboratorios de micología de baja complejidad. Objetivos: Evaluar el morfotipo de las colonias de levaduras en agar Sabouraud-trifeniltetrazolio como una herramienta para diferenciar C. dubliniensis de C. albicans. Métodos: Se evaluó la morfología de 126 aislamientos de C. albicans y C. dubliniensis y los resultados fueron comparados con los obtenidos utilizando métodos moleculares. Resultados: El método utilizado mostró una sensibilidad y una especificidad del 100% cuando se evaluó el color y la presencia o ausencia de un gran halo de micelio blanco. Conclusiones: La evaluación del morfotipo de las colonias en agar Sabouraud-trifeniltetrazolio puede ser utilizada como una nueva herramienta para diferenciar C. dubliniensis de C. albicans (AU)

Candida dubliniensis and Candida albicans differentiation by colony morphotype in Sabouraud-triphenyltetrazolium agar.

BACKGROUND: Candida dubliniensis is a germ tube and chlamydoconidia producing Candida species that may be misidentified as Candida albicans. Molecular-based methods are the most reliable techniques for C. albicans and C. dubliniensis differentiation. However, accurate, quick and inexpensive phenotypic tests are needed to be used in low-complexity mycology laboratories. AIMS: To evaluate colony morphotypes on Sabouraud-triphenyltetrazolium agar as a tool for C. dubliniensis and C. albicans differentiation. METHODS: The morphology of 126 C. albicans and C. dubliniensis strains was evaluated and compared with their identification by molecular methods. RESULTS: The method showed 100% sensitivity and specificity when color and the presence or absence of large white mycelial halo was evaluated. CONCLUSIONS: Colony morphotype on Sabouraud-triphenyltetrazolium agar should be considered as a new tool to differentiate C. dubliniensis and C. albicans.

Epidemiology and antifungal susceptibilities of yeasts causing vulvovaginitis in a teaching hospital.

Vulvovaginal candidiasis is one of the most common mycosis. However, the information about antifungal susceptibilities of the yeasts causing this infection is scant. We studied 121 yeasts isolated from 118 patients with vulvovaginal candidiasis. The isolates were identified by phenotypic and molecular methods, including four phenotypic methods described to differentiate Candida albicans from C. dubliniensis. Antifungal susceptibility testing was performed according to CLSI documents M27A3 and M27S4 using the drugs available as treatment option in the hospital. Diabetes, any antibacterial and amoxicillin treatment were statistically linked with vulvovaginal candidiasis, while oral contraceptives were not considered a risk factor. Previous azole-based over-the-counter antifungal treatment was statistically associated with non-C.albicans yeasts infections. The most common isolated yeast species was C. albicans (85.2 %) followed by C. glabrata (5 %), Saccharomyces cerevisiae (3.3 %), and C. dubliniensis (2.5 %). Fluconazole- and itraconazole-reduced susceptibility was observed in ten and in only one C. albicans strains, respectively. All the C. glabrata isolates showed low fluconazole MICs. Clotrimazole showed excellent potency against all but seven isolates (three C. glabrata, two S. cerevisiae, one C. albicans and one Picchia anomala). Any of the strains showed nystatin reduced susceptibility. On the other hand, terbinafine was the less potent drug. Antifungal resistance is still a rare phenomenon supporting the use of azole antifungals as empirical treatment of vulvovaginal candidiasis.

Molecular tools for cryptic Candida species identification with applications in a clinical laboratory.

Candida spp. includes more than 160 species but only 20 species pose clinical problems. C. albicans and C. parapsilosis account for more than 75% of all the fungemias worldwide. In 1995 and 2005, one C. albicans and two C. parapsilosis-related species were described, respectively. Using phenotypic traits, the identification of these newly described species is inconclusive or impossible. Thus, molecular-based procedures are mandatory. In the proposed educational experiment we have adapted different basic molecular biology techniques designed to identify these species including PCR, multiplex PCR, PCR-based restriction endonuclease analysis and nuclear ribosomal RNA amplification. During the classes, students acquired the ability to search and align gene sequences, design primers, and use bioinformatics software. Also, in the performed experiments, fungal molecular taxonomy concepts were introduced and the obtained results demonstrated that classic identification (phenotypic) in some cases needs to be complemented with molecular-based techniques. As a conclusion we can state that we present an inexpensive and well accepted group of classes involving important concepts that can be recreated in any laboratory.