Emergence of vanA Enterococcus faecium in Denmark, 2005-2015

Objectives: To describe the changing epidemiology of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis in clinical samples in Denmark 2005–15 according to species and van type, and, furthermore, to investigate the genetic relatedness of the clinical E. faecium isolates from 2015. Methods: During 2005–14, all clinical VRE isolates were tested for the presence of vanA, vanB, vanC genes by PCR. In 2015, all clinical VRE isolates were whole-genome sequenced. From the WGS data, the presence of van genes and MLST STs were extracted in silico. Core-genome MLST (cgMLST) analysis was performed for the vancomycin-resistant E. faecium isolates. Results: During 2005–15, 1043 vanA E. faecium, 25 vanB E. faecium, 4 vanA E. faecalis and 28 vanB E. faecalis were detected. The number of VRE was less than 50 isolates per year until 2012 to more than 200 isolates per year in 2013–15. In 2015, 368 vanA E. faecium and 1 vanB E. faecium were detected along with 1 vanA E. faecalis and 1 vanB E. faecalis. cgMLST subdivided the 368 vanA E. faecium isolates into 33 cluster types (CTs), whereas the vanB E. faecium isolate belonged to a different CT. ST203-CT859 was most prevalent (51%), followed by ST80-CT14 (22%), ST117-CT24 (6%), ST80-CT866 (4%) and ST80-CT860 (2%). Comparison with the cgMLST.org database, previous studies and personal communications with neighbouring countries revealed that the novel cluster ST203-CT859 emerged in December 2014 and spread to the south of Sweden and the Faroe Islands during 2015. Conclusions: VRE increased in Denmark during 2005–15 due to the emergence of several vanA E. faecium clones.