Identification of a Novel Clone, ST736, among Enterococcus faecium Clinical Isolates and Its Association with Daptomycin Nonsusceptibility

Abstract

ABSTRACTResistance to daptomycin in enterococcal clinical isolates remains rare but is being increasingly reported in the United States and worldwide. There are limited data on the genetic relatedness and microbiological and clinical characteristics of daptomycin-nonsusceptible enterococcal clinical isolates. In this study, we assessed the population genetics of daptomycin-nonsusceptibleEnterococcus faecium(DNSE) clinical isolates by multilocus sequence typing (MLST) and whole-genome sequencing analysis. Forty-two nonduplicate DNSE isolates and 43 randomly selected daptomycin-susceptibleE. faeciumisolates were included in the analysis. AllE. faeciumisolates were recovered from patients at a tertiary care medical center in suburban New York City from May 2009 through December 2013. The daptomycin MICs of the DNSE isolates ranged from 6 to >256 μg/ml. Three major clones ofE. faecium(ST18, ST412, and ST736) were identified among these clinical isolates by MLST and whole-genome sequence-based analysis. A newly recognized clone, ST736, was seen in 32 of 42 (76.2%) DNSE isolates and in only 14 of 43 (32.6%) daptomycin-susceptibleE. faeciumisolates (P< 0.0001). This report provides evidence of the association betweenE. faeciumclone ST736 and daptomycin nonsusceptibility. The identification and potential spread of this novelE. faeciumclone and its association with daptomycin nonsusceptibility constitute a challenge for patient management and infection control at our medical center.