Healthcare Administrator

GPCPC - E. faecalis/OE PNA FISH

For in vitro diagnostic use.

E. faecalis/OE PNA FISH™ (Cat. No. KT003) is a multicolor, qualitative nucleic acid hybridization assay intended for identification of Enterococcus faecalis and selected other enterococci (OE) from blood cultures.

E. faecalis/OE PNA FISH provides rapid identification of E. faecalis and selected other enterococci (OE) on smears made from positive blood cultures and is compatible with all major blood culture media.  The 2.5 hour fluorescence in situ hybridization (FISH) assay uses dual color fluorescently labeled peptide nucleic acid (PNA) probes that target the species-specific ribosomal RNA (rRNA) in E. faecalis and other enterococci. Results are visualized using fluorescence microscopy. Green fluorescing cells indicates E. faecalis while red fluorescing cells indicate other enterococci, including Enterococcus faecium. The absence of fluorescence indicates another species is present in the positive blood culture.

Features and Benefits

Results Reporting - Rapid Identification of GPCPC+ Blood Cultures

Once a blood culture turns positive, a Gram stain is performed. If the Gram stain reveals Gram-positive cocci in pairs and chains (GPCPC), E. faecalis/OE PNA FISH is performed and within a few hours, results are available and can be reported to the attending physician. Green fluorescing cells identify E. faecalis, while red fluorescing cells identify other enterococci. Green and red fluorescing cells identify a mixed culture with both E. faecalis and other enterococci, while the absence of fluorescence indicates non-enterococci GPCPC, e.g. streptococci.

Hospital-acquired infections due to Enterococcus species are on the rise in the United States. While infections with E. faecalis are susceptible to ampicillin and rarely resistant to vancomycin, infections with other enterococci, including E. faecium, are highly resistant to both ampicillin and vancomycin (VRE – vancomycin-resistant enterococci). See Figure 2. According to the Center for Disease Control and Prevention (CDC), VRE are responsible for 1 of every 3 infections in hospital intensive care units (ICU’s).(1,2)

E. faecalis/OE PNA FISH provides rapid identification of E. faecalis and other enterococci directly from GPCPC-positive blood cultures. Green fluorescing cells identify E. faecalis, which tend to be ampicillin susceptible, while red fluorescing cells identify other enterococci, including E. faecium, which tend to be highly vancomycin-resistant, i.e. VRE. See Figure 1. Results are available in a few hours, instead of days, allowing labs to quickly report results to physicians and pharmacists, helping to ensure optimal therapy for Enterococcal bloodstream infections.

Studies on Enterococcal Bloodstream Infections and E. faecalis/OE PNA FISH

Data presented by the University of Maryland Medical Center (UMMC) at the 106th ASM General Meeting in Orlando, Florida, showed that (1):·

• E. faecalis blood culture isolates were 100% susceptible to ampicillin and 95% susceptible to vancomycin.
• Other enterococci isolates, including E. faecium, were often resistant to both ampicillin and vancomycin, i.e. VRE.
• Of 14 patients with other enterococci in the study, 9/14 (64%) received ineffective initial therapy, with a median change to effective therapy of 3 days.
• For the patients receiving ineffective initial therapy, 6/7 (85%) eventually died.

Subsequent to the study, UMMC implemented a treatment algorithm for Enterococcal bloodstream infection that employs E. faecalis/OE PNA FISH to speed up identification of E. faecalis, other enterococci and rule-out enterococci from blood cultures containing GPCPC. According to the UMMC treatment algorithm, the following antibiotic therapies were administered, depending on the results of E. faecalis/OE PNA FISH (4).

• Ampicillin for E. faecalis (Positive - Green Fluorescing Cells)

• Linezolid for other enterococci (Positive – Red Fluorescing Cells)

• Ampicillin/Ceftriaxone for non-enterococci (Negative – No Fluorescing Cells)

Preliminary results from a prospective study were presented at the Infectious Diseases Society of America (IDSA) 2006 Annual Meeting in Toronto, Canada. Based on the results, the authors of the study found that using E. faecalis/OE PNA FISH for Enterococcal bloodstream infections (4):

• Allows for rapid and accurate identification of Enterococcus species
• Trends toward an earlier switch to ampicillin in E. faecalis isolates
• Significantly reduces time to correct therapy and mortality with E. faecium isolates

1. Johnson et al. Rapid Identification of Enterococcus Species in Positive Blood Cultures with Therapeutic Implications. 2006. Poster # C-147. 106th ASM, Orlando, Florida
2. Ibrahim et al. The influence of inadequate antimicrobial treatment of bloodstream infections on patient outcomes in the ICU setting. Chest. 2000 Jul;118(1):146-55. - Link
3. Centers for Disease Control and Preventation (CDC). Information for the public about VRE. http://www.cdc.gov/ncidod/dhqp/ar_VRE_publicFAQ.html
4. Toombs et al. Impact of Peptide Nucleic Acid (PNA) Fluorescence in situ Hybridization (FISH) for Enterococcal blood stream infections. Oral Abstract #131, IDSA 2006 Annual Meeting, Toronto, Canada