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API 20 strep identification system may incorrectly speciate enterococci with low level resistance to vancomycin
Lisa G Winston1, Szekim Pang, Barbara L Haller
1Department of Medicine, Division of Infectious Diseases, University of California, San Francisco/San Francisco General Hospital, San Francisco, CA 94110, USA. lisaw@itsa.ucsf.edu
Diagnostic Microbiology and Infectious Disease
|April 6, 2004
Summary
The API 20 Strep system inaccurately identified enterococci with low-level vancomycin resistance. Most isolates, initially classified as Enterococcus faecium, required further testing for correct species identification.
Area of Science:
- Clinical microbiology
- Antimicrobial resistance
Background:
- Accurate bacterial speciation is crucial for effective treatment, especially for resistant strains.
- Enterococci are common causes of healthcare-associated infections, with vancomycin resistance being a significant concern.
Purpose of the Study:
- To evaluate the accuracy of the API 20 Strep system for identifying enterococcal isolates with low-level vancomycin resistance.
- To determine the reliability of this system when faced with antimicrobial resistance.
Main Methods:
- API 20 Strep system was used for speciation.
- 46 enterococcal isolates with vancomycin Minimum Inhibitory Concentrations (MICs) of 16-32 microg/mL were tested.
- Further confirmatory testing was performed on discrepant results.
Main Results:
- All 46 isolates were initially identified as Enterococcus faecium by the API 20 Strep system.
- Subsequent testing revealed that 42 out of 46 isolates (91.3%) were incorrectly identified.
- The API 20 Strep system showed poor performance in correctly speciating these vancomycin-resistant enterococci.
Conclusions:
- The API 20 Strep system is unreliable for the accurate speciation of enterococci exhibiting low-level vancomycin resistance.
- Relying solely on the API 20 Strep system can lead to misidentification and potentially inappropriate clinical management.
- Additional diagnostic methods are necessary for reliable identification of vancomycin-resistant enterococci.