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Vancomycin-resistant Enterococcus raffinosus: molecular epidemiology, species identification error, and frequency of
W W Wilke1, S A Marshall, S L Coffman
1Department of Pathology, University of Iowa College of Medicine, Iowa City, 52242, USA.
Abstract:
Enterococcal blood stream infections are the third most common among all nosocomial blood stream infections in the United States and the occurrence of glycopeptide (vancomycin, teicoplanin) resistance in these isolates has markedly increased. Control of hospital-acquired infections with vancomycin-resistant enterococci requires high quality antimicrobial susceptibility test methods and species identification procedures as a supplement to epidemiologic investigation and appropriate infection control procedures. In this report, bacteremias caused by Enterococcus avium (BioMerieux Vitek, Hazelwood, MO, USA) were observed to be Enterococcus raffinosus infections (six of eight cases; 1.1% of all cases) when reference biochemical identification methods were applied. The vancomycin-susceptible E. raffinosis (two strains) and E. avium (two strains) had unique phenotypic and genotypic molecular profiles. In contrast, four vancomycin-resistant E. raffinosus strains (van A by polymerase chain reaction) from a single institution had the same phenotypic and molecular (PCR, PFGE, ribotyping) pattern, indicating clonal dissemination among four patients over a 66-day period. Clinical laboratories should be aware of the high probability that van A genes may be transferred from Enterococcus faecium or Enterococcus faecalis to other more rarely encountered Enterococcus species. Also contemporary, widely used commercial identification systems may fail to accurately identify those rare species. Errors appear to be most prevalent for E. avium, Enterococcus durans, and E. raffinosus based on the experience of the SCOPE Program.
Insights
Vancomycin-resistant enterococci (VRE) bloodstream infections are a growing concern. Commercial identification systems may misidentify rare enterococcal species, potentially impacting infection control and treatment strategies for VRE.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Molecular epidemiology
Background:
- Enterococcal bloodstream infections (BSIs) are a significant cause of hospital-acquired infections in the US.
- Increasing prevalence of glycopeptide resistance (e.g., vancomycin resistance) in enterococci complicates treatment.
- Accurate species identification and antimicrobial susceptibility testing are crucial for controlling VRE infections.
Purpose of the Study:
- To evaluate the accuracy of commercial identification systems for enterococcal species causing BSIs.
- To investigate the molecular characteristics and dissemination of vancomycin-resistant Enterococcus raffinosus strains.
- To highlight potential misidentification issues with rare enterococcal species.
Main Methods:
- Comparison of commercial identification system results with reference biochemical identification methods.
- Phenotypic and genotypic characterization of vancomycin-susceptible and resistant enterococcal isolates.
- Molecular techniques including polymerase chain reaction (PCR), pulsed-field gel electrophoresis (PFGE), and ribotyping were used.
Main Results:
- Eight cases initially identified as Enterococcus avium by a commercial system were reclassified as Enterococcus raffinosus using reference methods.
- Four vancomycin-resistant E. raffinosus strains (vanA gene positive) from one institution shared identical molecular profiles, suggesting clonal spread.
- Vancomycin-susceptible E. avium and E. raffinosus isolates exhibited distinct molecular patterns.
Conclusions:
- Commercial identification systems may inaccurately identify rare enterococcal species like E. avium and E. raffinosus.
- The vanA gene, conferring vancomycin resistance, may transfer to less common enterococcal species.
- Awareness of potential identification errors is critical for effective infection control and epidemiological surveillance of VRE.