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Published on: February 10, 2011
Disk diffusion-based method aids in the detection of vanM-positive Enterococcus faecium with low vancomycin minimum
Jue Wang1,2, Pei Li1,2, Lin Xin1,2
1Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China.
Abstract:
We first reported the vanM vancomycin resistance gene in enterococci in Shanghai, China in 2006 and later found it to be the predominant van gene in vancomycin-resistant enterococci (VRE). In this study, we successively collected 1292 Enterococcus faecium and Enterococcus faecalis strains from in- and outpatients at Huashan Hospital, Fudan University and found that nearly all of the isolates (1290/1292) were vancomycin-sensitive determined by the VITEK 2 system. However, using a modified macromethod-based disk diffusion test, 10 E. faecium isolates that were previously determined to be vancomycin-sensitive by the VITEK 2 system were found to have colonies in the vancomycin disk inhibition zone. Pulse-field gel electrophoresis results showed that each randomly selected colony in the inhibition zone belonged to the same clone as the original strain. All 10 isolates were later found to be vanM-positive. The disk diffusion-based method may aid in the detection of vanM-positive E. faecium with low vancomycin minimum inhibitory concentrations and prevent missing the detection of vancomycin sensitivity-variable enterococci.
Insights
A modified disk diffusion test identified vancomycin resistance in 10 Enterococcus faecium strains previously classified as sensitive. This method helps detect vanM-positive strains with low vancomycin minimum inhibitory concentrations, preventing misdiagnosis of vancomycin-resistant enterococci.
Area of Science:
- Microbiology
- Antimicrobial Resistance
- Clinical Diagnostics
Background:
- Vancomycin resistance in enterococci (VRE) is a significant healthcare concern.
- The vanM gene is a predominant cause of VRE in Shanghai, China.
- Standard diagnostic systems may misclassify certain vancomycin-sensitive strains.
Purpose of the Study:
- To evaluate a modified disk diffusion method for detecting vancomycin resistance in Enterococcus faecium.
- To identify vanM-positive Enterococcus faecium isolates with low vancomycin minimum inhibitory concentrations.
- To improve the detection of vancomycin sensitivity-variable enterococci.
Main Methods:
- Collection and VITEK 2 system susceptibility testing of 1292 Enterococcus faecium and Enterococcus faecalis isolates.
- Modified macromethod-based disk diffusion testing for vancomycin susceptibility.
- Pulse-field gel electrophoresis for clonal analysis.
- vanM gene detection using molecular methods.
Main Results:
- 1290 out of 1292 isolates were vancomycin-sensitive by VITEK 2.
- 10 Enterococcus faecium isolates showed growth within the vancomycin disk zone, indicating potential resistance.
- All 10 isolates were confirmed vanM-positive.
- Pulse-field gel electrophoresis confirmed isolates with zone growth were the same clone as the original strain.
Conclusions:
- A modified disk diffusion test can detect vanM-positive Enterococcus faecium with low vancomycin MICs that may be missed by automated systems.
- This method enhances the identification of vancomycin sensitivity-variable enterococci.
- Improved diagnostic approaches are crucial for managing antimicrobial resistance.
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