Ann Clin Microbiol.  2015 Sep;18(3):76-81. 10.5145/ACM.2015.18.3.76.

Epidemiology and Molecular Characterization of Vancomycin-Resistant Enterococcus faecalis

• Kim J
• Choi KH
• Kim YS
• Lee WG

• KMID: 2052100
• DOI: http://doi.org/10.5145/ACM.2015.18.3.76

Abstract

BACKGROUND
Vancomycin-resistant Enterococci (VRE) infections are caused by Enterococcus faecium in about 90% of the cases but can also be caused by Enterococcus faecalis. Thus, this study investigates factors that cause a low isolation rate of vancomycin-resistant E. faecalis (VREfs). To this end, the authors study the clinical traits, resistant gene structure, genomic classification, and molecular characteristics of the virulent factor.
METHODS
From January 2001 through September 2011, 17 vanA-containing E. faecalis isolates were collected from hospitalized patients at Ajou University Hospital in Korea. Identification, antimicrobial susceptibility testing, and PCR of van and esp genes were performed. Pulsed-field gel electrophoresis (PFGE) was used for strain typing. PCR and sequencing of the internal regions of Tn1546 were performed for structural analysis of the van gene.
RESULTS
Of 4,235 VRE infections, 3,918 (92.5%) were caused by E. faecium, and 95 (2.2%) were caused by E. faecalis. In 67% of VREfs infections, there was a preceding occurrence of E. faecium infection. All isolates were of genotype vanA. Our isolates were divided into three types according to the distribution of IS elements integrated into Tn1546 (types I to IIb). The PFGE results showed no clonal relatedness among isolates.
CONCLUSION
Our study found that VREfs infections affect patients who have experienced vancomycin-resistant E. faecium. (VREfm) infection or undergo invasive procedures. The VREfs seems to involve the horizontal transfer of Tn1546 transposon from VREfm.

Keyword

IS1216V; IS1542; Tn1546; Vancomycin-resistant Enterococcus faecalis

MeSH Terms

Classification
DNA Transposable Elements
Electrophoresis, Gel, Pulsed-Field
Enterococcus faecalis*
Enterococcus faecium
Enterococcus*
Epidemiology*
Genotype
Humans
Korea
Polymerase Chain Reaction
DNA Transposable Elements

Figure

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  Fig. 1. The number of isolated enterococcal species according to 11 years. Abbreviations: VREfm, vancomycin-resistant Enterococcus faecium; VREfs, vancomycin resistant-Enterococcus faecalis.

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  Fig. 2. Tn1546 type of 17 vanA positive E. faecalis isolates. The positions of the genes and open reading frames (orf1 and orf2) and the direction of transcription are marked by big arrows at the top. Inverted triangles represent IS elements. The position of the first nucleotide upstream and the first nucleotide downstream from the IS insertion sites are depicted. Small arrows indicate the transcriptional orientation of the inserted IS elements. Deletions are indicated by dotted lines. Adapted from “Genetic rearrangements of Tn1546-like elements in vancomycin-resistant Enterococcus faecium isolates collected from hospitalized patients over a seven-year period,” by Park IJ, Lee WG, Lim YA and Cho SR, J Clin Microbiol 2007;45:3903-8. Adapted with permission.

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