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Published on: July 9, 2012
Improved detection of vanB2-containing enterococcus faecium with vancomycin susceptibility by Etest using oxgall
1Microbiology Department, Austin Hospital, Studley Rd., Heidelberg, Victoria, Australia. Elizabeth.Grabsch@austin.org.au
Journal of Clinical Microbiology
|April 25, 2008
Summary
We identified "low-MIC vancomycin-resistant enterococci" (LM-VRE) with the vanB gene. Supplementing agar media with oxgall improved detection of these challenging vancomycin-resistant enterococci (VRE) strains.
Area of Science:
- Microbiology
- Molecular Biology
- Clinical Diagnostics
Background:
- Vancomycin-resistant enterococci (VRE) pose a significant healthcare threat.
- Certain VRE strains exhibit vanB gene presence but low vancomycin Minimum Inhibitory Concentrations (MICs), complicating detection.
- Accurate identification of VRE is crucial for infection control.
Purpose of the Study:
- To investigate the molecular basis of vancomycin resistance in Enterococcus faecium isolates with low vancomycin MICs.
- To evaluate methods for improving the phenotypic detection of these difficult-to-identify VRE strains.
Main Methods:
- Molecular characterization (PCR, DNA sequencing) of vanB-containing Enterococcus faecium isolates.
- Testing supplemented agar media (Mueller-Hinton agar and brain heart infusion agar with oxgall) for enhanced VRE detection.
- Assessing sensitivity and specificity of supplemented media using characterized VRE and susceptible strains.
Main Results:
- All low-MIC VRE isolates contained the vanB operon associated with transposon Tn1549.
- No sequence variations were found in the vanB ligase gene compared to the prototype.
- Supplementation of Mueller-Hinton agar and brain heart infusion agar with 10 g/liter oxgall significantly improved Etest detection of LM-VRE.
- Both oxgall-supplemented media demonstrated 100% sensitivity and specificity for detecting vancomycin resistance after 48 hours of incubation.
Conclusions:
- Supplementing standard agar media with oxgall is a valuable strategy for improving the detection of vancomycin-resistant enterococci, particularly those with low vancomycin MICs.
- Laboratories relying on phenotypic methods for VRE detection should consider incorporating oxgall into their media formulations.
- This approach can aid in the timely and accurate identification of VRE, supporting effective infection control measures.
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