Clonal structure of Enterococcus faecalis isolated from Polish hospitals: characterization of epidemic clones

Abstract

To study the population structure of Enterococcus faecalis from Polish hospitals, 291 isolates were typed by pulsed-field gel electrophoresis and a novel multilocus sequence typing scheme (P. Ruiz-Garbajosa et al., J. Clin. Microbiol. 44:2220-2228, 2006). The isolates originated from geographically widespread medical institutions and were recovered during a 10-year period (1996 to 2005) from different clinical sources. The analysis grouped the isolates into five epidemic and 71 sporadic clones. The importance of the previously identified global clonal complexes CC2 and CC9 was corroborated by our findings that two of the Polish epidemic clones, A and J, were classified into these clonal complexes (CCs). However, the two most predominant clones, C (ST40) and F (CC87), did not cluster in the aforementioned CCs and may represent novel epidemic CCs. These clones may have emerged in Central Europe. Clone F, carrying glycopeptide resistance determinants of VanA or VanB phenotypes, caused several outbreaks in hematology units and appeared to be the most prevalent clone in recent years in Poland. Antimicrobial susceptibility testing and additional tests for pathogenicity-related phenotypes (hemolysin and gelatinase production) and genes (asa1 and esp) were performed to further characterize these epidemic clones. Multidrug resistance, glycopeptide resistance, presence of asa1, and production of hemolysin appeared to be statistically significant features related to epidemicity. Production of gelatinase was significant for two of the epidemic clones, whereas presence of the esp gene was not specific for the epidemic clones.

FIG. 1.

The clonal structure of the collection of 291 E. faecalis isolates collected from 1996 to 2005 in hospitals in Poland. (A) The three-dimensional snapshot depicting the similarity of PFGE patterns obtained with the in silico analysis. Each figure represents a single isolate; shapes correspond to PFGE types identified by visual interpretation of PFGE. (B) eBURST analysis of the MLST data. The epidemic clones are called as in panel A; the sizes of points are in direct proportion to numbers of isolates of each ST in the online database (http://efaecalis.mlst.net).

FIG. 2.

Characteristics of the epidemic and sporadic PFGE clones. MDR, multidrug resistance; Cyl, hemolysin production; GelE, gelatinase production; asa1, presence of the asa1 gene; esp, presence of the esp gene; VRE, presence of the vanA or vanB gene.