Korean J Lab Med.  2009 Aug;29(4):299-306. 10.3343/kjlm.2009.29.4.299.

Microbiological and Epidemiological Characteristics of Vancomycin-dependent Enterococci

• Hwang K
• Sung H
• Namgoong S
• Yoon NS
• Kim MN

• KMID: 1096922
• DOI: http://doi.org/10.3343/kjlm.2009.29.4.299

Abstract

BACKGROUND: Vancomycin-dependent enterococci (VDE) are clinically equivalent to vancomycin-resistant enterococci (VRE), but more difficult to detect. This study was purposed to characterize VDE microbiologically and epidemiologically.
METHODS
The patients from whom VDE were detected from April 2007 to March 2008 were investigated. For available isolates, minimal inhibitory concentrations (MICs) of and the levels of dependence on vancomycin and teicoplanin were measured by E test (AB Biodisk, Sweden), and a test for reversion of VDE to non-dependent VRE (NDVRE) and pulsed field gel electrophoresis (PFGE) were performed. Patients' demographic and clinical findings were reviewed via electronic medical records.
RESULTS
VDE were recovered from 6 (2.2%) of 272 patients carrying VRE during this study period. All patients were already colonized or infected by VRE and treated with vancomycin for 13 to 107 days. VDE were isolated from pleural fluid (one), urine (four), and stool (one). All isolates carried vanA with vancomycin MICs of >256 microgram/mL, but two of them had intermediate susceptibilities to teicoplanin. Because 4 VDE isolates were reverted to NDVRE with single passage, vancomycin dependence was measurable for only two isolates as equal and above 0.064 and 0.5 microgram/mL respectively, and was reverted after 5 and 7 passages, respectively. Six VDE isolates showed no related clones in PFGE analysis, and 3 of 4 available pairs of initial VRE isolates and subsequent VDE isolates were identical clones.
CONCLUSIONS
VDE were not rare and seemed to emerge independently from VRE with a prolonged use of vancomycin. Vancomycin-dependence was reverted within several passages.

Keyword

Vancomycin dependency; Vancomycin resistance; Enterococcus

MeSH Terms

Adult
Aged
Electrophoresis, Gel, Pulsed-Field
Enterococcus/classification/drug effects/*isolation & purification
Female
Humans
Infant
Male
Microbial Sensitivity Tests
Middle Aged
Urinary Tract Infections/diagnosis/microbiology
Vancomycin/*pharmacology
Vancomycin Resistance

Figure

• 

  Fig. 1. Clinical features of 6 cases growing VDE. ᅭ periods of hospital stay with numbers denoting hospital days; ⬇, periods of vancomycin therapy; ᐁ, isolation of VRE; ▬, isolation of VDE. ⬩—-⬩, periods of hospital stay of sa- me ward for patient 2 and 3; ⬩…⬩, periods of hospital stay of same ward for patient 4 and 5. Abbreviations: W, wound; S, stool; U, urine; PF, pleural fluid.

• 

  Fig. 2. Disk diffusion test for vancomycin dependent enterococci isolated from patient 4 showing thick growth only in the area near by vancomycin (VA30) and teicoplanin (TEC30) disks but no growth around linezolid (LZD30) and quinupristin/dalfopristin (SYN15) disks (A). Vancomycin (VA) and teicoplanin (TP) E tests showing dependence on 0.064 μg/mL or more and MIC of 256 μg/mL against vancomycin and dependency of 0.016 μg/mL or more and MIC of 12 μg/mL against teicoplanin (B).

• 

  Fig. 3. Pulsed field gel electrophoretic profiles of SmaI-digested chromosomal DNA of six vancomycin-dependent enterococci and five vancomycin-resistant enterococci. Lane M, Lambda DNA concatomer (New England Biolabs, Beverly, MA, USA); Lane 1, vancomycin-dependent E. avium from patient 1; Lane 2-4, initial vancomycin-resistant E. faecium, subsequent vancomycin-dependent E. faecium and post-VDE vancomycin-resistant E. faecium from patient 2; Lane 5 and 6, initial vancomycin-resistant E. faecium and subsequent vancomycin dependent E. faecium from patient 3; Lane 7 and 8, initial vancomycin-resistant E. faecium and subsequent vancomycin-dependent E. faecium from patient 4; Lane 9 and 10, initial vancomycin-resistant E. faecium and subsequent vancomycin-dependent E. faecium from patient 5; Lane 11, vancomycin-dependent E. faecium from patient 6.

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