Molecular characterisation of outbreak-related strains of vancomycin-resistant Enterococcus faecium from an intensive care unit in Beijing, China

https://doi.org/10.1016/j.jhin.2009.02.014Get rights and content

Summary

We investigated an outbreak of vancomycin-resistant Enterococcus faecium affecting 14 patients in a 20-bed intensive care unit (ICU) between September 2006 and August 2007 (incidence: 3.56 cases per 1000 ICU patient days). Eighteen isolates of vanA type E. faecium were analysed by pulsed field gel electrophoresis, which showed 14 types overall. Multilocus sequence typing (MLST) identified eight different sequence types (STs) (ST78, ST117, ST203, ST316, ST362, ST363, ST364 and ST365), including four new types (ST362, ST363, ST364 and ST365) and 17 strains belonged to clonal complexes CC17. Sixteen of these carried the esp gene. Eighteen Tn1546-like elements encoding vanA-type VRE were classified into three types (types I to III) and all of them contained both IS1216V and IS1542 insertions. Vancomycin resistance of 14 vanA type E. faecium isolates was transferred at a frequency of 1.3 × 10−6 to 6.4 × 10−5 between E. faecium strains during filter mating. Our findings indicate that conjugative dissemination of Tn1546-like elements among CC17 E. faecium occurred during the outbreak in this ICU.

Introduction

The isolation of vancomycin-resistant enterococci (VRE) was first reported in 1988 in the UK and France, and shortly thereafter, VRE was detected in hospitals in the USA. Since then, VRE have emerged with unanticipated rapidity and are now encountered in most hospitals.1, 2, 3 Patients in intensive care units (ICUs) are frequently affected, mainly because they are severely ill, and heavily exposed to multiple antibiotics and exogenous colonisation pressure.4

To our knowledge this is the first study that has characterised the phenotypic and molecular features of VRE isolated from an intensive care unit in Mainland China.

Section snippets

Bacterial strains and culture media

Eighteen isolates of vanA type Enterococcus faecium isolated from 15 patients within one year were used in this study (Table I). Enterococci were grown in Todd–Hewitt broth (THB). Type strains E. faecium WHO03 and E. faecalis WHO14 having VanA and VanB phenotypes were used as controls.

Antimicrobial susceptibility testing

Glycopeptide resistance levels were determined by the agar dilution method. An overnight culture of the strains grown in Mueller–Hinton broth was diluted 100-fold with fresh broth. A total of 100 μL of each

Isolation and characterisation of vanA-type vancomycin-resistant E. faecium

During an outbreak affecting 14 patients in a 20-bed ICU (incidence 3.56 cases per 1000 ICU patient-days) between September 2006 and August 2007, 18 strains of vancomycin-resistant E. faecium were isolated. These were the first VRE to be isolated from that ICU. We screened the stool of all patients in the ICU on 7 September 2006 and five of 14 patients carried VRE. One year after the first VRE strain was isolated we screened stool samples on August 6 2007 and four of 16 patients were found

Discussion

Recently, genetic population studies have shown that a majority of vancomycin-resistant E. faecium strains associated with nosocomial infections worldwide are part of the same lineage called CC17.14 CC17 strains are generally resistant to ampicillin and carry genes for putative virulence factors, such as esp.15 Our study supports this observation and the outbreak strains showed an antibiotic resistance profile and virulence genes similar to those described for CC17. It has been argued that

Acknowledgements

We thank H. Grundmann for reviewing the manuscript.

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