Journal List > Ann Clin Microbiol > v.18(3) > 1078541

Kim, Choi, Kim, and Lee: Epidemiology and Molecular Characterization of Vancomycin-Resistant Enterococcus faecalis

초록

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 vancomy-cin-resistant E. faecalis (VREfs). To this end, the au-thors 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 div-ided 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 af-fect patients who have experienced vancomycin-re-sistant E. faecium. (VREfm) infection or undergo in-vasive procedures. The VREfs seems to involve the horizontal transfer of Tn1546 transposon from VREfm.

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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.
acm-18-76f1.tif
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.
acm-18-76f2.tif
Table 1.
Strain Specimen esp gen analysis Tn 1546 type PFGE based dendrogram
100% 80% 60% 40% 20% 0%
J1 Catheter Neg IIb @@@image@@@@
J3 Wound Pos IIa
J12 Wound Pos IIa
J2 Wound Neg IIa
J4 Urine Pos IIa
J5 Urine Pos IIa
J8 Blood Neg IIa
J6 Wound Pos I
J9 Urine Neg IIb
J10 Catheter Neg IIb
J13 Wound Pos IIa
J17 Urine Neg IIa
J15 Wound Pos IIa
J14 Pus Neg IIa
J16 Wound Pos IIa
J7 Urine Pos IIa
J11 Urine Pos IIb

No presence of the esp gene;

Presence of the esp gene.

Abbreviation: PFGE, pulsed field gel electrophoresis.

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