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Evaluation of Vitek system for susceptibility testing of Enterococcus faecium isolates
Hae Kyung Lee1, Yeon-Joon Park, Hi Jeong Kwon
1Department of Clinical Pathology, College of Medicine, Catholic University, Seoul, Korea.
Annals of Clinical and Laboratory Science
|March 25, 2004
Summary
Imipenem susceptibility testing for Enterococcus faecium using the Vitek system is unreliable. Penicillin and ampicillin results can predict imipenem activity, but Vitek imipenem MICs require retesting via agar dilution.
Area of Science:
- Clinical microbiology
- Antimicrobial susceptibility testing
Background:
- Imipenem shows potential for treating mixed infections involving enterococci.
- Current guidelines lack standardized susceptibility testing for imipenem against enterococci.
- Predictive value of other antimicrobial results for imipenem activity is not established.
Purpose of the Study:
- To evaluate the reliability of the Vitek system for imipenem susceptibility testing in Enterococcus faecium.
- To assess the correlation between imipenem in vitro activity and that of penicillin and ampicillin.
- To determine if existing susceptibility data can predict imipenem efficacy.
Main Methods:
- Collected 52 Enterococcus faecium isolates from clinical specimens (urine, wounds).
- Utilized the Vitek system for antimicrobial susceptibility testing.
- Performed agar dilution method for confirmatory testing.
Main Results:
- Vitek system showed 0% major and 36.5% very major errors for imipenem MICs.
- Ampicillin and penicillin MICs from Vitek were reliable (0% major errors).
- In vitro activity of penicillin and ampicillin accurately predicted imipenem activity.
Conclusions:
- The Vitek system's imipenem MICs for Enterococcus faecium are unreliable.
- Agar dilution method is recommended for retesting Vitek imipenem MICs when discordant with penicillin/ampicillin results.
- Penicillin and ampicillin susceptibility can guide imipenem treatment decisions for enterococcal infections.