Are Commercial Systems Used for the Identification of Yeasts Enough Alone?: A Case Report

Abstract

Infections developing due to Trichosporon species especially in immunosuppressed patients have started to increase also in our country as well as in the world. Some difficulties have been encountered in identification and treatment of Trichosporon spp. which are relatively more resistant to antifungal treatment. Accurate and rapid identification of yeast species is very important to ensure determination of the appropriate antifungal agent in treating these infections. Due to long time span and intense effort required, determination using conventional methods has recently been replaced by common use of commercial systems allowing rapid identification. However, the commercial systems used to determine yeasts are reported to have higher correct identification rates for frequently isolated species, whereas lower rates for rarer species. In this report, we aimed to address that the commercial systems are enough alone for identification by evaluating a case of urinary tract infection with a positive urine culture yielding yeasts. A urine culture revealed dry, wrinkled, waxy, pink, yeast-like colonies on blood agar and eosin-methylene blue agar after a 24-hour incubation. These colonies were identified as Cryptococcus sp. using VITEK (R) 2 (bioMerieux, Marcy l'Etoile, France) system. On the other hand, this isolate had been demonstrated as Trichosporon asahii by microscopic and macroscopic appearance, carbohydrate assimilation test results and urease positivity. Additionally, antifungal susceptibility of isolate was determined using microdilution (amphotericin B, voriconazole, fluconazole) and Etest (R) (AB Biodisk, Solna, Sweden) methods (caspofungin, anidulafungin) according to Clinical Laboratory Standards Institute M27-A3 standard. In conclusion, this case report demonstrated that there is a need for confirmation of results with conventional methods for determination of rare species such as Trichosporon spp. identified with commercial systems based on biochemical properties, and antifungal susceptibility tests should be performed in clinical microbiology laboratories.