Evaluation of the Yeast Traffic Light PNA FISH Probes for Identification of Candida Species from Positive Blood Cultures

Abstract

The Yeast Traffic Light PNA FISH kit (YTL) correctly identified Candida spp. in 207/216 (96%) positive blood cultures. Discordant results were seen with known cross-reacting species and cultures containing Candida lambica and Rhodotorula mucilaginosa. The YTL provides rapid, reliable identification of the five common Candida species found in blood cultures. Candida species are the leading cause of fungemia in both community-acquired and nosocomial infections (2). Two recent studies have shown that the use of PNA FISH probes to identify yeast in blood cultures decreases patient costs by directing appropriate antimicrobial therapy. Forrest et al. used the FDA-cleared Candida albicans PNA FISH kit (AdvanDx, Woburn, MA) for identification of C. albicans in 72 positive blood cultures (3). Rapid results allowed for a significant reduction in the use of caspofungin, with an overall cost savings of $1,729 per patient. In a similar study, Alexander and colleagues used a decision analytic model and showed an average savings of $1,837 per patient with the use of PNA FISH (1). Since the publication of these and other studies (6, 7, 9), additional probe kits have been cleared by the FDA, including the C. albicans/Candida glabrata PNA FISH kit and the Yeast Traffic Light PNA FISH kit (YTL).The performance of the C. albicans/C. glabrata PNA FISH kit has been previously reported (8). The YTL is a next-generation, three-probe system which is FDA cleared for the rapid identification of C. albicans/Candida parapsilosis, C. glabrata/Candida krusei and Candida tropicalis from positive blood cultures. Initially, the YTL was cleared using a 90-min probe hybridization step. Recently, a 30-min hybridization time was cleared, which further reduced the turnaround time to less than 2 h after the blood culture bottle signals as positive. In this study, we report the performance characteristics of the YTL kit using both the 90-and 30-min hybridization times. The reliability of the kit for the identification of the five claimed Candida species was evaluated, and the specificity of the probes was challenged using a wide variety of other yeast genera and species.Fifty-four blood cultures that were positive by Gram stain (44 yeast and 10 bacteria) were tested on the day of signal or were aliquoted and frozen at Ϫ20°C before testing as per the YTL product insert. In order to increase the number and diversity of yeasts tested, an additional 118 yeasts were inoculated into 5 ml of human red blood cells (Innovative Research, Navi, MI), and the simulated blood specimen was then placed into a Bactec MYCO/F lytic blood culture bottle (Becton Dickinson, Sparks, MD), incubated at 37°C, and tested with the YTL kit on the day that the bottle signaled positive. Subcultures of an additional 44 unusual yeast species grown on inhibitory mold agar (Becton Dickinson) were also tested for potential cross-reactivity of nontargeted yeast. The reference method for identification of the yeast used in the study was Sanger sequencing of the D2 large-subunit (LSU) RNA g...

Advances in Identification of Clinical Yeast Isolates by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…An advantage of PNA FISH compared to chromogenic medium is that it does not rely on growth of the isolate for presumptive identification. This enables the identification of select species of yeast directly from positive blood cultures in as little as 2 h with 97.5% to 100% sensitivity (25,26). While more specific than chromogenic medium, PNA FISH is also limited in the number of species that can be identified, and cross-reactivity of probes with other species of yeast has been reported (25).…”

“…A number of FDA-cleared assays based on PNA FISH technology for the detection of yeasts are available and have been evaluated (25)(26)(27)). An advantage of PNA FISH compared to chromogenic medium is that it does not rely on growth of the isolate for presumptive identification.…”

Cost-Effectiveness Analysis of Multiplex PCR with Magnetic Resonance Detection versus Empiric or Blood Culture-Directed Therapy for Management of Suspected Candidemia

“…We assumed that a rapid identification method, such as the FilmArray blood culture identification panel (BioFire Diagnostics, UT) or the Yeast Traffic Light PNA-FISH method (AdvanDX, MA), was used to identify Candida spp. detected in positive blood cultures, providing species identification in 1 to 2 h (23)(24)(25). If a T2Candida test had already been performed, this rapid identification method would not be necessary, and the associated laboratory costs were reduced accordingly (see "Cost Considerations," below).…”

In vitro diagnosis of sepsis: a review

“…100 The technique is based on fluorescently labeled oligonucleotide probes specific for ribosomal RNA, which have been used to detect .95% of bacteria and fungi in BC. 101,102 The most commonly used target in prokaryotes is 16S rRNA. 103 The assay allows the identification of many pathogens in only 2.5-3 hours.…”