Detection of a Newcfr-Like Gene,cfr(B), in Enterococcus faecium Isolates Recovered from Human Specimens in the United States as Part of the SENTRY Antimicrobial Surveillance Program

Abstract

ABSTRACTTwo linezolid-resistantEnterococcus faeciumisolates (MICs, 8 μg/ml) from unique patients of a medical center in New Orleans were included in this study. Isolates were initially investigated for the presence of mutations in the V domain of 23S rRNA genes and L3, L4, and L22 ribosomal proteins, as well ascfr. Isolates were subjected to pulsed-field gel electrophoresis (just one band difference), and one representative strain was submitted to whole-genome sequencing. Gene location was also determined by hybridization, andcfrgenes were cloned and expressed in aStaphylococcus aureusbackground. The two isolates had one out of six 23S rRNA alleles mutated (G2576T), had wild-type L3, L4, and L22 sequences, and were positive for acfr-like gene. The sequence of the protein encoded by thecfr-like gene was most similar (99.7%) to that found inPeptoclostridium difficile, which shared only 74.9% amino acid identity with the proteins encoded by genes previously identified in staphylococci and non-faeciumenterococci and was, therefore, denominated Cfr(B). When expressed inS. aureus, the protein conferred a resistance profile similar to that of Cfr. Two copies ofcfr(B) were chromosomally located and embedded in a Tn6218similar to thecfr-carrying transposon described inP. difficile.This study reports the first detection ofcfrgenes inE. faeciumclinical isolates in the United States and characterization of a newcfrvariant,cfr(B).cfr(B) has been observed in mobile genetic elements inE. faeciumandP. difficile, suggesting potential for dissemination. However, further analysis is necessary to access the resistance levels conferred bycfr(B) when expressed in enterococci.