Sentinel Surveillance Reveals Emerging Daptomycin-Resistant ST736 and Multiple Mechanisms of Linezolid Resistance in Enterococci in the United States.

and with resistance to daptomycin and/or linezolid are emerging globally. We present the genomic characterization of daptomycin- and linezolid-resistant and surveillance isolates from the United States, 2013-2016. Daptomycin resistance was low among (2/364, 0.5%) and (17/344, 5%). The majority (71%, 12/17) of daptomycin-resistant isolates belonged to the emerging ST736 clone and contained mutations in and previously associated with resistance. However, 1/2 and 3/17 did not contain these mutations previously associated with daptomycin resistance. Linezolid resistance was rare among (1/364, 0.3%) and (2/344, 0.6%). These two isolates, one of which was also resistant to daptomycin and vancomycin, contained the 23S rRNA nucleotide mutation (G2576T) associated with linezolid resistance. Long-read sequencing revealed the linezolid-resistant isolate contained chromosomal- and plasmid-encoded copies of . The chromosomal was located on the recently described Tn multiresistance transposon. The second copy of was encoded on an ∼65 kb mosaic plasmid, with component regions sharing high sequence identity to -encoding multiresistance plasmids of animal origin. The -encoding plasmid contained open reading frames predicted to encode proteins associated with a pheromone-responsive plasmid transfer system, and filter mating experiments confirmed the plasmid was conjugative. Continued surveillance of enterococci is necessary to assess the prevalence and trends of daptomycin and linezolid resistance in the United States, characterize resistance mechanisms and how they transfer, and monitor for emerging sequence types associated with resistance.