Rapid identification of bacteria and candida using pna-fish from blood and peritoneal fluid cultures: a retrospective clinical study

Dana M Harris,D Jane Hata

doi:10.1186/1476-0711-12-2

Abstract

BackgroundPeptide nucleic acid fluorescent in situ hybridization (PNA-FISH) is a rapid and established method for identification of Candida sp., Gram positive, and Gram negative bacteria from positive blood cultures. This study reports clinical experience in the evaluation of 103 positive blood cultures and 17 positive peritoneal fluid cultures from 120 patients using PNA-FISH. Our study provides evidence as to potential pharmaceutical cost savings based on rapid pathogen identification, in addition to the novel application of PNA-FISH to peritoneal fluid specimens.MethodsIdentification accuracy and elapsed time to identification of Gram positives, Gram negatives, and Candida sp., isolated from blood and peritoneal fluid cultures were assessed using PNA-FISH (AdvanDx), as compared to standard culture methods. Patient charts were reviewed to extrapolate potential pharmaceutical cost savings due to adjustment of antimicrobial or antifungal therapy, based on identification by PNA-FISH.ResultsIn blood cultures, time to identification by standard culture methods for bacteria and Candida sp., averaged 83.6 hours (95% CI 56.7 to 110.5). Identification by PNA-FISH averaged 11.2 hours (95% CI 4.8 to 17.6). Overall PNA-FISH identification accuracy was 98.8% (83/84, 95% CI 93.5% to 99.9%) as compared to culture. In peritoneal fluid, identification of bacteria by culture averaged 87.4 hours (95% CI −92.4 to 267.1). Identification by PNA-FISH averaged 16.4 hours (95% CI −57.3 to 90.0). Overall PNA-FISH identification accuracy was 100% (13/13, 95% CI 75.3% to 100%). For Candida sp., pharmaceutical cost savings based on PNA-FISH identification could be $377.74/day. For coagulase-negative staphylococcus (CoNS), discontinuation of vancomycin could result in savings of $20.00/day.ConclusionsIn this retrospective study, excellent accuracy of PNA-FISH in blood and peritoneal fluids with reduced time to identification was observed, as compared to conventional culture-based techniques. Species-level identification based on PNA-FISH could contribute to notable cost savings due to adjustments in empiric antimicrobial or antifungal therapy as appropriate to the pathogen identified.

Highlights

Peptide nucleic acid fluorescent in situ hybridization (PNA-FISH) is a rapid and established method for identification of Candida sp., Gram positive, and Gram negative bacteria from positive blood cultures
9 blood and 6 peritoneal fluid culture bottles had been spiked with Candida sp. or other yeasts in the laboratory in order to increase sample numbers to statistically meaningful levels specific for the pathogen
In signal-positive blood culture bottles containing Gram positive bacteria, the following species were identified by PNA-FISH: 34 coagulase-negative Staphylococcus [coagulase-negative staphylococcus (CoNS)], 10 S. aureus, 5 E. faecalis, 5 E. faecium

Summary

Introduction

Peptide nucleic acid fluorescent in situ hybridization (PNA-FISH) is a rapid and established method for identification of Candida sp., Gram positive, and Gram negative bacteria from positive blood cultures. Our study provides evidence as to potential pharmaceutical cost savings based on rapid pathogen identification, in addition to the novel application of PNA-FISH to peritoneal fluid specimens. Bloodstream associated infections (BSI) are the 10th leading cause of death in the U.S [1]; this rate has increased by 78% over the last 2 decades. New detection technologies for organism identification from blood culture such as real-time PCR, DNA microarrays, matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF), and peptide nucleic acid fluorescent in situ hybridization (PNA-FISH) for detection of Candida, Gram positive, and Gram negative organisms may increase organism identification accuracy, and significantly reduce time to result [5]

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