Evaluation of Peptide Nucleic Acid Fluorescent In Situ Hybridization (PNA FISH) Method in the Identification of Candida Species Isolated From Blood Cultures

In recent years, increased number of patients who are hospitalized in intensive care units, received immunosuppressive therapy and treated with broad-spectrum antibiotics that can lead an increase in the incidence of systemic candidiasis. In these patients, the most common clinical manifestation is candidemia. Since the identification of Candida species isolated from blood cultures is time consuming by conventional (morphological and biochemical) methods, rapid, reliable and accurate methods are needed. For this purpose novel systems have been developed to identify the agent directly. The aim of this study was to evaluate the peptide nucleic acid fluorescent in situ hybridization (PNA FISH) method for the identification of Candida species by comparing with the conventional methods. A total of 50 patients who were admitted to Erciyes University Medical Faculty Hospital clinics and followed with prediagnosis of systemic fungal infections whose blood cultures were positive for the yeasts between July 2011 and July 2012 were included in the study. The conventional identification of Candida isolates was performed by considering macroscopic and microscopic morphology, germ tube test, cycloheximide sensitivity, urease activity and carbohydrate assimilation patterns with API 20C AUX (bioMerieux, France) test. PNA FISH method was conducted by the use of a commercial kit namely Yeast Traffic Light PNA FISH (AdvanDx, USA). According to morphological and biochemical characteristics (conventional methods), 19 (38%) out of 50 Candida isolates were identified as C.albicans, 12 (24%) as C.glabrata, five (10%) as C.parapsilosis, five (10%) as C.kefyr, four (8%) as C.krusei, two (4%) as C.guilliermondii, two (4%) as C.tropicalis and one (2%) as C.lusitaniae. On the other hand, 24 (48%) of the isolates were identified as C.albicans/C.parapsilosis (with green fluorescence), 16 (32%) as C.glabrata/C.krusei (with red fluorescence) and one (%2) as C.tropicalis (with yellow fluorescence) properly, however one C.tropicalis strain was misidentified as C.albicans by PNA FISH method. Other eight (16%) strains which were not presented in the evaluation panel of PNA FISH kit (5 C.kefyr, 2 C.guillermondii and 1 C.lusitaniae), gave no fluorescence and determined as other Candida spp. According to this, when the species that could be detected with the kit (C.albicans, C.parapsilosis, C.glabrata, C.krusei and C.tropicalis) were considered, the concordance rate with the conventional methods was determined as 97.6% (41/42) and the total evaluation rate for all the species was 84% (41/50). In conclusion, the most frequent isolated species from blood cultures in our hospital was C.albicans, followed by C.glabrata and C.parapsilosis. Since PNA FISH testing is a practical, reliable and rapid (resulted in 90 minutes) method for the identification of Candida strains at species level isolated from blood cultures, it was thought to be useful in routine laboratories. However, further comparative studies are required with large number of strains with the consideration of cost-effectiveness