Evaluation of the PNA FISH technology for yeast identification directly from positive blood cultures. An Italian experience

Abstract number: P1911

Farina C., Andreoni S., Bonetti C., Casella P., Conte M., Fazii P., Lombardi G., Luzzaro F., Manso E., Marone P., Morazzoni C., Passera M., Perin S., Rocchetti A., Sanna S., Viganò E.

Objectives: Yeasts are responsible for the majority of fungemias. Non albicansCandida spp. are frequently difficult to treat because of their sensitivity patterns. The PNA (peptide nucleic acid) FISH (fluorescence in situ hybridization) technology is designed to discriminate among medically important yeasts in blood samples, allowing clinicians to begin a proper empirical therapy.

Aim of the study was to evaluate the performance of PNA-FISH to directly identify yeasts from blood cultures.

Methods: Centers: 14 Microbiology labs of Italian Public Hospitals were included in a network coordinated by the Medical Mycology Committee – Associazione Microbiologi Clinici Italiani.

Samples: 72 blood cultures positive for yeasts at direct Gram stain; 4 blood negative cultures as control.

Technology: Yeast Traffic Light PNA FISH® AdvanDx, Woburn, USA able to discriminate C. albicans/C. parapsilosis, C. tropicalis and C. krusei/C. glabrata.

Reading: Lecture done in double by two different microbiologists and supervision by a third one.

Control: In case of discrepancy, complete reprocessing of the samples.

Results: The agreement between the traditional and the FISH techniques was 94,7% (72/76: 4 neg and 68 pos cultures). Complete agreement was observed for 33 Candida albicans/parapsilosis (C. albicans, 27; C. parapsilosis, 6); 17 Candida glabrata/krusei (C. glabrata, 16; C. krusei, 1); 7 Candida tropicalis; 6 C. albicans + C. glabrata. The test was negative in 5 cases of yeasts recognized by Gram staining but not-included in the FISH pattern (C. lusitaniae 2; C. guilliermondii 1; C. neoformans 1; G. capitatum 1).

Discrepancies occurred in 3 samples apparently positive only for C. albicans but mixed (C. albicans + C. tropicalis, 2; C. albicans + C. glabrata, 1). One case of a mixed culture (C. tropicalis + C. glabrata) at the traditional identification resulted caused by C. glabrata only.

Finally, sensitivity of the FISH technique evaluated for 5 Candida species was 98,6%, and specificity 100%.

Conclusion: Distinguishing which yeast is causing fungemia, and whether the infection is due to multiple species, is important for the selection of antifungal therapy, particularly if results can be quickly transmitted to clinicians. The PNA FISH® testing is a very useful approach because the test discriminates between groups of Candida species with different susceptibility pattern, particularly against azoles and echinocandins, and only 90 minutes are requested after the Gram stain reading.

Session Details

Date: 07/05/2011
Time: 00:00-00:00
Session name: Abstracts of 21st ECCMID / 27th ICC
Location: Milan, Italy, 7 - 10 May 2011
Presentation type:
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