Emergence of mosaic plasmids harboring Tn1546-ermBelement inStaphylococcus aureusisolates

Abstract

ABSTRACTAntimicrobial resistance inStaphylococcus aureusis a major problem and the acquisition of resistance genes may occur by horizontal gene transfer (HGT). The transposon, an important means of HGT, is recognized as a mobile genetic element that can integrate in plasmids, replicate and transfer to other strains. We have previously reported a novel structure of theEnterococcus faecium-originated Tn1546-ermBelement inS. aureus. The emergence of the Tn1546-like element is an emerging problem that requires continuous monitoring. In the present study, we expand the examination of Tn1546-ermBelement toermB-positive methicillin-susceptibleS. aureus(MSSA) (n = 116) andermB-positive methicillin-resistantS. aureus(MRSA) (n = 253) during a 16-year period, from 2000 to 2015. PCR mapping showed that 10 MSSA and 10 MRSA carried the Tn1546-ermBelement. The 10 MSSA belonged to three sequence types (ST), ST7 (n = 6), ST5 (n = 3), and ST59 (n = 1), and the 10 MRSA belonged to two STs, ST188 (n = 8) and ST965 (n = 2). Since only clonal complex 5 (including ST5, ST85, ST231, and ST371) MRSA, ST8 MRSA and ST5 MSSA have been previously reported to carry Tn1546plasmids, this is the first report describing the presence of the Tn1546-ermBelement in ST7/5/59 MSSA and ST188/965 MRSA. Plasmid sequencing revealed that the Tn1546-ermBelement was harbored by five different mosaic plasmids. In addition to resistance genes, some plasmids also harbored toxin genes.