Emergence of clonal complex 17 Enterococcus faecium in The Netherlands

Abstract

The global emergence of vancomycin-resistant Enterococcus faecium has been characterized as the clonal spread of clonal complex 17 (CC17) E. faecium. CC17 was defined upon multilocus sequence typing and is characterized by resistance to quinolones and ampicillin and the presence of the enterococcal surface protein (Esp) in the majority of isolates. The recently noticed increased incidence of vancomycin-susceptible CC17 E. faecium infections in our hospital initiated a nationwide study to determine ecological changes among enterococcal infections. The data and strain collections were obtained from 26 (38%) and 9 (14%) of 66 microbiology laboratories in The Netherlands. E. faecium and E. faecalis were distinguished by multiplex PCR; all E. faecium isolates were genotyped by multiple-locus variable-number tandem-repeat analysis (MLVA), and the presence of esp was identified by PCR. Average numbers of ampicillin-resistant enterococcal isolates from normally sterile body sites per hospital increased from 5 +/- 1 in 1994 to 25 +/- 21 in 2005. Among all enterococcal bloodstream infections, the proportions of ampicillin-resistant E. faecium (AREF) increased from 4% in 1994 to 20% in 2005 (P < 0.001). All E. faecalis isolates were susceptible to ampicillin, whereas 78% of the E. faecium isolates were resistant (49% of these contained esp). Genotyping revealed that 86% of AREF isolates belonged to CC17, including four dominant MLVA types found in > or = 3 hospitals, accounting for 64% of the AREF isolates. Infections caused by CC17 E. faecium has increased nationwide, especially in university hospitals due to the clonal spread of four MLVA types, and seems associated with acquisition of the esp gene.

FIG. 1.

Average annual numbers of invasive Amp^r enterococci per hospital. Error bars denote standard deviations. University and nonuniversity hospitals were compared. For each year, the numbers of hospitals that provided data are indicated.

FIG. 2.

Annual distribution of five predominant MTs.

FIG. 3.

eBURST clustering of 18 MLST profiles, indicated by an arrow, representing 27 isolates from present study, with 313 MLST profiles representing 855 E. faecium isolates from the database (www.mlst.net). Each ST is represented as a node; the relative size of each node is indicative of its prevalence among the isolates, and lines connect single-locus variants (STs that differ in only one of the seven housekeeping genes). Dashed lines indicate connections between double-locus variants. The sources of specific clusters of STs are indicated, including CC17 comprising hospital outbreaks and clinical isolates. Clin_inf, isolates from clinical sites (mainly blood) from hospitalized patients; Hosp_outbreak, hospital outbreak isolates; Hosp_surv, feces isolates from hospitalized patients without an enterococcal infection and not associated with an enterococcal hospital outbreak; Human_comm, feces isolates from human volunteers not connected to hospitals.

FIG. 4.

Comparison of the annual distribution of esp-positive and -negative isolates.